Prince Charles will not 'willingly step down from his destiny' to be king, a royal biographer has claimed.

Yesterday it was announced Britain will get an extra Bank Holiday in 2022 to celebrate the Queen's Platinum Jubilee, when Her Majesty will become the first British monarch to have reigned for 70 years.

Robert Lacey, who recently released biography Battle of the Brothers and has acted as a historian on the Netflix drama The Crown, told Good Morning Britain it's a clear sign that the monarch, 94, is 'determined to go on to the end'.

Prince Charles, who turns 72 tomorrow, is the longest-serving heir-apparent to the British throne and will be the oldest-ever King when he is crowned, but Lacey said he doesn't believe the Prince of Wales has any intention of stepping aside.

However, he said that given the Queen has engendered such loyalty and respect, the 'popular' Duke and Duchess of Cambridge might be more fitting replacements.

'The Queen's jubilee certainly shows the Queen is determined to go on to the end,' said Lacey.

'But there is such loyalty and respect for the Queen, when we look to the future and say who could duplicate that in the future, could it be King Charles and Queen Camilla?

'Or would it much better be William and Kate who are already the focus of enormous popularity and are clearly stepping into the role of future sovereign.

'I myself don't think he would willingly step down from the destiny he has waited for so long.'

However, Robert feels that Charles has recently been stepping into the role of Britain's future king, after he and Prince William represented the Royal Family at last week's Remembrance Sunday service at London's Cenotaph, with Charles laying a wreath on his mother's behalf.

He also referenced the Prince of Wales and Duchess of Cornwall's trip to Germany this weekend, which will be the first joint official overseas visit since the coronavirus pandemic began.

Charles and Camilla will fly to Berlin to attend the Central Remembrance Ceremony on Sunday to commemorate the country's annual National Day of Mourning, Clarence House has said.

Charles' presence at the ceremony will be the first time a member of the royal family has taken part in the event.

Robert acted as a historical consultant on the upcoming fourth season of The Crown, and warned the forthcoming episodes, which will detail 'the most difficult years' in the royal family's modern life, could get 'pretty ugly'.

He told: 'We made a great effort, I'm only the historical consultant in a huge team on The Crown, but we made a huge effort to understand Charles and where he was coming from.

'With the fact that right from the beginning it was likely he would spend a long time in waiting and so it has proved.

'Now season four starts with the most difficult years in the royal family's modern life, the 1980s, the beginning of the marriage to Diana the breakdown of that marriage, the role of camilla and in any marriage breakdown things get pretty ugly I'm afraid.'