Watch: Prince Philip death: The Duke of Edinburgh dies, aged 99
Prince Philip once told a friend he was "ready to die" and said he did not want to make it to his 100th birthday.
Gyles Brandreth, the Duke of Edinburgh's biographer, said Philip had "no desire" to "cling onto life unnecessarily".
Recalling one of his conversations with Philip at Buckingham Palace, Brandreth wrote in the Daily Mail: "'I'm quite ready to die,' the duke said to me. 'It's what happens — sooner or later.' Again, he smiled.
"'I certainly don't want to hang on until I am 100, like Queen Elizabeth [the Queen Mother]. I can't imagine anything worse.
"'I have absolutely no desire to cling on to life unnecessarily. Ghastly prospect.'"
And in his long life, he did not hold regrets, Brandreth said.
When once asked if life had been "fun" or "enjoyable" he "screwed up his eyes" and answered: "I enjoyed flying very much. I sometimes think I should have joined the Air Force instead of the Navy."
He said there was "there's no point in having regrets".
Former MP Brandreth noted the change in the duke in the last 10 years of his life, saying he "appeared to me to be more contented in late life than he had been in middle age, more at ease with himself, with his family, and with the world".
There'd been a particular turnaround in the relationship between duke and heir, with Prince Charles showing affection where he'd previously indicated he felt abandoned as a child.
Watch: Prince Charles: We will miss Prince Philip enormously
When Charles spoke to Jonathan Dimbleby in the early 1990s, he suggested he'd felt neglected at home, but by 2012, the Prince of Wales was giving much more glowing reports of his mother and father – something Brandreth said the duke was touched by.
Though Prince Philip had himself spoken about difficulties between him and his son. Brandreth said Philip told him Charles was "precious, extravagant and lacking in the dedication necessary to make a good king".
However that was not how he felt by the time he died.
He also revealed why Prince Philip and the Queen did not sit on the thrones provided for them on the boat during the 2012 Diamond Jubilee pageant on the River Thames.
Brandreth said the duke had told him: "We'd have looked like Mr and Mrs Beckham, wouldn't we?"
The Thames Diamond Jubilee pageant involved more than 600 boats, a world record event, but the day was somewhat marred by the continual rain.
The Queen and Philip were on board the royal barge throughout the afternoon, as they watched the procession with Charles, Camilla, the Duke and Duchess of Cambridge and Prince Harry.
Prince Philip's funeral is set to be held on Saturday afternoon, with a smaller, COVID regulated event taking place.
The 800 strong guest list has had to be whittled down to 30 people, to fit in with the current guidelines.
The Duke of Edinburgh's coffin will follow a short procession through Windsor Castle's grounds before the service inside St George's Chapel.
Watch: Prince Philip and the Queen's marriage