Sir David Attenborough is to tell all about the late Queen Elizabeth II in a new BBC documentary produced to mark what would have been her 100th birthday.

The presenter will remember the former monarch as he knew her alongside contributions from celebrities, close friends and members of the Royal Family.

While Sir David pays tribute to her 'regal' air, her childhood friend Baroness Glenconner will recall facing cheering crowds on the Buckingham Palace balcony at her coronation.

The documentary, titled Queen Elizabeth II: Her Story, Our Century, is set to air at 9pm on BBC One on Sunday and will also feature a contribution from Queen Camilla.

In a clip from the show, Sir David said of Elizabeth II: 'The reality of being Queen was very evident to her at all times, It wasn't something that she put on like a coat or something. It was in the marrow of her bones. She was regal.'

Born just weeks apart from the Queen in 1926, Sir David enjoyed a close friendship with the late monarch that spanned from six decades. 

The environmentalist, who was knighted by the Queen in 1985, appeared on The Queen's Green Planet in 2018 and produced her televised Christmas Day address for various years in the 1980s and 1990s.

He featured in a segment of the BBC's Platinum Party at the Palace in 2022 to celebrate the Queen's Platinum Jubilee.

In 2020, Sir David was appointed a Knight Grand Cross of the Order of St Michael And St George for services to television broadcasting and to conservation in the Queen's Birthday Honours list.

After her death, he captured the mood of the country when he said: 'The whole nation is bereaved'.

Elsewhere the documentary hears from Baroness Glenconner, who was a close childhood friend to both the late Queen and her sister Margaret.

She was selected as one of her maids of honour during Elizabeth II's coronation in 1953.

Recalling stepping out onto the balcony of Buckingham Palace after the service, Baroness Glenconner said: 'People were absolutely thrilled. I remember going on the balcony and the crowd packed together, roaring. 

'You could actually feel it on one. And every time she turned to go they wouldn't let her.'

The documentary takes a look back at the long life of the last monarch, who died aged 96 on September 8, 2022, and her legacy.

Its other contributors include Dame Helen Mirren, Barack Obama, Dame Sheila Hancock and Queen Camilla. 

It is billed as a blend of archive footage, news interviews and contemporary reflection.

The late Queen would have turned 100 on April 21. 

Royal Mail is also set to mark the milestone with a dozen special edition stamps.

A main set of eight stamps will feature photographs from memories in Queen Elizabeth II's life, from delivering her first radio broadcast in 1940 aged 14 to her 1953 coronation balcony appearance at Buckingham Palace. 

And her love of horses and dogs has also not gone unrepresented - as four other stamps, in a miniature sheet, show her at stages in her life with pets or thoroughbreds.

A presentation pack including all 12 stamps costs £22.50.

Catherine Catton, head of factual entertainment and events, said: 'Queen Elizabeth II: Her Story, Our Century explores the life of her Late Majesty Queen Elizabeth II through the lens of a century of change and offers an important reflection on how modern Britain has been shaped.'