King Charles III has paid a touching tribute to his mother, echoed her pledge of lifelong service and spoken proudly of his sons in his first address to the nation as monarch.

Speaking in a pre-recorded message aired just under 24 hours after the death of his "darling Mama" was made public, Charles began by sharing his profound sorrow and immense gratitude for Queen Elizabeth II.

A gratitude he said would be felt alongside grief throughout the United Kingdom and the Commonwealth.

LIVE UPDATES: King Charles III delivers first speech since the death of the Queen

"Throughout her life, Her Majesty the Queen, my beloved mother, was an inspiration, an example to me and to all my family

"And we owe her the most heartfelt debt any family could to their mother, for her love, affection, guidance, understanding and example."

He harked back to the Queen's famous declaration of lifelong service, made at just 21 and widely considered by many who spoke since her death to have been well and truly fulfilled.

Sitting solemnly next to a picture of the Queen, mirroring her last Christmas message delivered next to a picture of her fallen husband, Prince Philip, Charles renewed that pledge in his name.

EXPLAINER: What happens next? Historic day for Britain as King Charles III succeeds to the throne

"As the Queen herself did with such unswerving devotion, I too now solemnly pledge myself throughout the remaining time God grants me to uphold the constitutional principles at the heart of our nation," he said.

"And wherever you may live in the United Kingdom, or in the realms and territories, across the world, and whatever may be your background or beliefs I shall endeavour to serve you with loyalty, respect, and love, as I have throughout my life."

READ MORE: When to expect the coronation of the new king

The King said he was proud to crown his son William as the Prince of Wales, along with his succession as the Duke of Cornwall, titles both inherited from Charles.

"With Catherine beside him, our new Prince and Princess of Wales will, I know, continue to inspire and lead our national conversations, helping to bring the marginal to the centre ground, where vital help can be given," he said.

The King also expressed his love for Prince Harry and Meghan, the Duchess of Sussex, in their life overseas.

READ MORE: King Charles III greets crowds at Buckingham Palace with Queen Consort

He ended his message with a touching tribute to the Queen.

"To my darling Mama, as you begin your last great journey to join my dear Papa, I want simply to say this," he said.

"Thank you. Thank you for your love and devotion to our family and to the family of nations.

"You have served so diligently all these years. May flights of angels sing thee to thy rest."

King Charles III and Camilla, Queen Consort, have been greeted by a rapturous crowd outside the gates of Buckingham Palace on their return to London following the death of Queen Elizabeth II.

A loud shout of "God save the King" erupted as the couple arrived at the palace they will now call home, and Charles began warmly greeting the waiting masses.

There were smiles, handshakes and even a few kisses as the new monarch met some of his subjects for the first time as King, before entering the palace for the first time in his new role.

READ MORE: Details of period of mourning announced

In one way, it was simply a grieving man returning home, but royal commentators said the moment signified much more.

BBC home editor Mark Easton said one of the King's security guards followed him closely, telling the waiting masses to put their phones down and "enjoy the moment".

"This was a huge moment — don't forget that — because this was the first time that the new King met his people on that line outside Buckingham Palace," he said.

"Interesting that he drove to the gates of the palace, but didn't drive in. He stopped. 

"His first first job that he felt as soon as he got to what will now be his home at Buckingham Palace was to leave the car and go and meet his people. 

"And he met them in a very direct way. As you were saying he was kissed on the hand. He was kissed on the cheek by one woman. His hands were grabbed."

The new monarch and his wife had taken off about 12.30pm on Friday (9.30pm AEST) from Aberdeen International Airport in Scotland, where they had travelled to be with the Queen at her Balmoral home before her death.

The King later held his first meeting with Prime Minister Liz Truss, just a few days after his mother had welcomed the new Tory leader into office.

On Saturday, September 10, Charles will officially succeed to the throne in front of the Accession Council, although he already became King immediately upon his mother's death.

As per tradition dating back to the 15th century, the garter king of arms, who is responsible for governing royal heraldry in England, Wales and Northern Ireland, will step out onto the balcony at St James's Palace and officially proclaim Charles as the new King.

A 41-gun salute at London's Hyde Park will follow.

Charles is due to address the UK at 6pm tonight (3am AEST).

St Paul's Cathedral in London will hold an evening service to mark the Queen's death at 6pm local time, which will be open to the public. Members of the royal family will not attend.

In the days that follow, the new King will attend a joint session involving both houses of the British Parliament and embark on a tour of the UK, visiting Scotland, Northern Ireland and Wales.

The King's coronation will not occur for weeks, if not months. The Anglican religious service, presided over by the Archbishop of Canterbury is the symbolic ascension of the heir to the throne.

Queen Elizabeth II and her husband Prince Philip enjoyed a lasting relationship for more 70 years, a union that far outlasted the marriages of three of her four children: Charles, Anne and Andrew.

"He has been quite simply my strength and stay all these years," the Queen said on their 50th wedding anniversary.

The pair, who were third cousins, met when Elizabeth was 13, and it's said she instantly fell head over heels for Philip in 1939.

READ MORE: The life and achievements of Queen Elizabeth II

The handsome 18-year-old naval cadet was detailed to entertain Elizabeth for a day.

Phillip serving the Royal Naval College in Dartmouth and during the war, the two exchanged letters.

The couple married in Westminster Abbey in 1947.

Together they took their royal duties across the Commonwealth including, a visit to Kenya on their way to Australia and New Zealand.

Though they were very much in love, they couldn't have anticipated what was to come when Elizabeth would become Queen.

READ MORE: Australians can expect 'shock to system' from new King

Following the death of King George VI, her Majesty took the crown in 1952.

Although their relationship was professional and about service, it was also about love.

When Philip died in 2021 at the age 99, Elizabeth described his passing as leaving a "huge void" in her life, according to their son, Andrew.

"The Queen as you would expect is an incredibly stoic person and she described his passing as a miracle and she is contemplating, I think that's the way I would put it," Andrews previously told reporters.

READ MORE: Prince Harry and Prince William reunited in grief at Prince Philip's funeral

"She described it as having left a huge void in her life, but we, the family, the ones that are closer, are rallying around to make sure that we're there to support her."

As they were in life, Queen Elizabeth II and Prince Philip are now together in death.

Following her funeral, the date of which is yet to be announced, Her Majesty will be buried in the King George VI Memorial Chapel at St George's Chapel in Windsor.

With Associated Press

Landmarks across Australia have been lit up in the colour purple to mark the passing of Queen Elizabeth II.

Melbourne's MCG, Flinders Street Station and the Sydney Opera House are among those locations glowing in regal purple.

Her majesty, has died aged 96, peacefully at her Balmoral home in Scotland.

LIVE UPDATES: King Charles III delivers first speech since the death of the Queen

Premier Daniel Andrews paid tribute to Queen Elizabeth II, remembering her as someone like "no monarch before her".

"(It will be) a token of deep respect and gratitude for Queen Elizabeth II, her service, dignity, and grace," he said.

Other landmarks across Australia will also be illuminated tonight in honour of Queen Elizabeth II.

READ MORE: After a lifetime of preparation, Charles takes the throne

Premier Dominic Perrottet said the tribute on the Opera House was a symbolic gesture on behalf of the NSW Government.

"The tribute on the sails will recognise Her late Majesty's immense contribution to our state and nation, a fitting tribute as she officially opened the Sydney Opera House in 1973," Perrottet said.

The world mourns the Queen as the UK wakes up to a new era and a new monarch. Here's what we can expect to happen tonight.

A teenage driver who killed two mothers in a crash at Waihola last year is a “disgraceful” human being, a grieving mother says.The 17-year-old earlier pleaded guilty to dangerous driving causing the deaths of Charlene Hong Hue Phuong…

Prime Minister Jacinda Ardern expects King Charles III will stay politically neutral, despite making his opinions known on several issues in the past. Speaking to Newstalk ZB’s Heather du Plessis-Allan this evening, Ardern also…

Current and former Australian prime ministers have paid tribute to the Queen following her death early this morning.

Anthony Albanese led the charge and said "Australian hearts go out to the people of the United Kingdom", remarking that she always performed her duty with "fidelity, integrity and humour".

Queen Elizabeth II completed sixteen tours to Australia in her lifetime, each one greeted by cheering crowds.

LIVE UPDATES: Aussie politicians pay tribute to the Queen

"With the passing of Queen Elizabeth the Second, an historic reign and a long life devoted to duty, family, faith and service has come to an end," Albanese said.

"The Government and the people of Australia offer our deepest condolences to the Royal Family, who are grieving for a beloved mother, grandmother and great-grandmother—the person whom for so long was their greatest inner strength.

"Australian hearts go out to the people of the United Kingdom who mourn today, knowing they will feel they have lost part of what makes their nation whole.

"There is comfort to be found in Her Majesty's own words: 'Grief is the price we pay for love'."

READ MORE: The life and achievements of Queen Elizabeth II

A number of former Australian Prime Ministers have also paid tribute to the late Monarch, including Kevin Rudd who praised her sense of duty.

"Therese and I had the opportunity to meet with the Queen on several occasions over the years, and it was clear from those conversations that her affection for Australia was as profound as it was enduring," he said.

"Whether republicans or monarchists, Australians will be deeply affected by this news."

Former prime minister Tony Abbott said today is a sombre day as the world mourns "one of the greatest every human lives".

"She made history, she personified history and she had seen things and done things and met people beyond that of anyone else ever and that made her special," he said.

"She will be remembered as someone who had our well-being very much in her mind and in her heart, and I think she demonstrated this time and time again by the steady stream of messages that she sent to us in good times and in bad.

"She congratulated us on our victories. She sorrowed with us in our disasters. She was with us in our disasters. She was with us every step of the way and I think she appreciated that down to Earth, have a go, egalitarian Australian spirit."

READ MORE: From assassination plots to making Aeroguard famous: A look back on the Queen's visits to Australia

John Howard praised Her Majesty's commitment to duty and her service to the UK and the world.

"She saw service, commitment to duty, doing the right thing constitutionally and always understanding she was monarch by the free will and consent of her people not by any divine right," he said.

Former prime minister Paul Keating said the Queen's "stoicism and moralism" bound her to the job of being a monarch.

"She was an exemplar of public leadership, married for a lifetime to political restraint, remaining always, the constitutional monarch," his statement read.

"Her exceptionally long, dedicated reign is unlikely to be repeated; not only in Britain, but in the world generally."

Julia Gillard praised Her Majesty as a "remarkable role model" after ascending to the throne at a young age but accepting the role with "grace, devotion and dignity".

"The Queen has been a powerful presence for as long as many of us can remember," she said.

"I am in awe of the Queen's legacy and remember my own personal meetings with her fondly.

"She was strong and steadfast, but also kind and had an engaging sense of humour."

READ MORE: A timeline of Queen Elizabeth II's recent health issues

Opposition Leader Peter Dutton joined other political leaders in paying tribute to Queen Elizabeth II.

"Never in modern history has there been a more dignified monarch, a more dutiful leader, or a more decent human than Her Majesty Queen Elizabeth II," Dutton said in a statement.

"An extraordinary life which touched so many has sadly come to an end. The last page has been inked on an exceptional reign."

Dutton described the Queen as "gentle, kind, and much-loved".

"Her Majesty Queen Elizabeth II lived through the pivotal events of the 20th and 21st centuries – wars and conflicts, depression and recession, the end of empire and decolonisation, the race to the moon and the attainment of civil rights, the brilliance of Olympic Games and the barbarity of terrorism," he said.

"She led Britain through the darkest of days and through the times of triumph."

EXPLAINED: 'London Bridge is down' – What happens now?

Governor-General David Hurley described the Queen as "remarkable", saying that Australians can take inspiration from her tireless work ethic.

"I join with all Australians in mourning Her Majesty The Queen's passing and in remembering her lifetime of tireless service. She was a truly remarkable person," he said.

"When I reflect on my own memories – she was my Queen for my whole life – I think of Her Majesty's dignity and her compassion. Her dedication and tireless work ethic. And her selflessness and unwavering commitment to the people that she served. To us.

"Her death will sadden all Australians and will be felt around the world.

"As we mourn, we should also take inspiration from and give thanks for the remarkable contribution Her Majesty has made."

From Buckingham Palace to Aberdeen airport and an hour's drive away to Balmoral Castle, photos highlight the solemnity of the occasion.

England is in mourning following the death of Her Majesty Queen Elizabeth II, but it's not just the Brits who have shed a tear – tributes have been laid bare across the world.