Grand, solemn and with a few personal touches, King Charles III's coronation at Westminster Abbey was a choreographed performance a millennium in the making.

Just eight months ago, Charles, 74, was at the imposing Gothic abbey for the state funeral of his mother Queen Elizabeth II, his face etched with grief.

On Saturday, it was serious with the sense of responsibility, as he walked slowly up the aisle towards his destiny, some 70 years after he became Elizabeth's heir.

Behind him, his nine-year-old grandson Prince George, second in line to the throne, helped carry the monarch's heavy velvet robe with three other young pages.

Guests bowed or curtsied as Charles and his wife Queen Camilla passed.

Among the 2,300 guests were foreign leaders and their representatives, pop stars and television presenters, as well as ordinary members of the public, rewarded for their work in the community.

Not everyone among the guests was a staunch monarchist.

Northern Ireland's first minister-designate Michelle O'Neill is from the republican Sinn Fein party, which not so long ago was the political wing of the IRA paramilitary group that assassinated Charles's great-uncle and mentor Louis Mountbatten in 1979.

Charles is separately the king of 15 Commonwealth states. Australia's Prime Minister Anthony Albanese and New Zealand's PM Chris Hipkins, who both attended, want their countries to abandon constitutional monarchy and become republics.

- Service -

However, the focus was not on politics but on the deeply religious service, its rites and rituals developed over the centuries from the time of the first coronation at the abbey in 1066.

A 14-year-old chorister from the Chapel Royal greeted the sovereign "in the name of the King of Kings".

"In His name and after His example, I come not to be served but to serve," Charles replied.

Throughout, respectful silence filled the abbey with the sweet smell of wildflowers brought from all four corners of the United Kingdom at the request of the king, a lifelong environmentalist.

Looking on from the front row was Charles's elder son and heir, Prince William, his wife Kate, and their two youngest children, Princess Charlotte, eight, and Prince Louis, five.

On the third row was William's brother Prince Harry, whose rift with the family has deepened since he left for California and began issuing repeated public criticisms of royal life.

Like Charles before him, William's role is mapped out. Kneeling, he pledged his allegiance to the man he will one day succeed -- before touching the crown and planting a kiss on his father's cheek in a tender gesture.

Harry's future, now focused on the United States and a world of big-money deals for books and television series, is less certain.

But Charles would have known Harry was there in the congregation, which was asked to recognise him as their "undoubted king".

"God save King Charles," came the reply.

- 'God save the king' -

The most sacred part of the ancient ceremony -- the anointing with holy oil -- was hidden from public view and even from the television and stills cameras discreetly positioned around the church.

The anticipation built as he discarded his Robe of State, and donned a sumptuous golden silk cloak, the Supertunica, over the Colombium Sindonis -- a simple white linen tunic symbolic of humility.

Then, more royal attributes: the Imperial Mantle; a golden orb; shimmering sceptres; and a ring to symbolise the union of the monarch and his people.

With Charles in the battered Coronation Chair, Scotland's ancient Stone of Destiny underneath, Archbishop of Canterbury Justin Welby took the solid gold St Edward's Crown in his hands carefully.

"King of kings and Lord of lords, bless, we beseech thee, this Crown and so sanctify thy servant Charles upon whose head this day thou dost place it for a sign of royal majesty," he said.

Lifting it high, he then brought the priceless bejewelled crown down on Charles's head for the first and what will be the only time in his reign, taking a moment to ensure it did not slip.

"God save the King" the congregation thundered and the sound of cheers from the crowds outside filtered into the abbey.