King Charles III told friends he was "utterly elated" after Prince William's birth, which he said was "an astonishing experience and one that has meant more to me than I could ever have imagined."
Prince William celebrated his birthday on June 21, 41 years after Charles sat by Princess Diana's bedside as she gave birth.
The king expressed his personal feelings about becoming a father in letters to friends, including Hugh and Emilie van Cutsem, which were published in 1994 as part of authorized biography The Prince of Wales: A Biography, by Jonathan Dimbleby.
In a 1982 letter to the couple, Charles wrote: "I got back here just before midnight—utterly elated but quite shattered. I can't tell you how excited and proud I am.
"He really does look surprisingly appetizing and has sausage fingers just like mine."
Charles' hands are known to swell and it is not the only time he has joked about his sausage fingers. During a 2012 visit to Australia, he talked about being "so jetlagged that I feel a few sausages short of a barbie."
And he is not the only one as Prince William joked in a speech on Charles' 70th birthday, in November 2018, that he hoped the king's "sausage fingers" would stop writing letters in order to free up time to see his grandchildren, according to the Daily Mail.
After William's birth, Charles also wrote to his godmother, Patricia Brabourne: "The arrival of our small son has been an astonishing experience and one that has meant more to me than I could ever have imagined.
"As so often happens in this life, you have to experience something before you are in a true position to understand or appreciate the full meaning of the whole thing.
"I am so thankful I was beside Diana's bedside the whole time because by the end of the day I really felt as though I'd shared deeply in the process of birth and as a result was rewarded by seeing a small creature which belonged to us even though he seemed to belong to everyone else as well!
"I have never seen such scenes as there were outside the hospital when I left that night—everyone had gone berserk with excitement... since then we've been overwhelmed by people's reactions and thoroughly humbled."
The official announcement of William's birth read: "The Princess of Wales was safely delivered of a son at 9:03 p.m. today. Her Royal Highness and her child are both doing well."
Charles and Diana named him William Arthur Philip Louis, with the final name a tribute to Louis Mountbatten, the king's great uncle who played a mentoring role in his life.
Patricia Brabourne was Mountbatten's daughter and Charles asked her permission to use William's name as an opportunity to pay tribute three years after Mountbatten was assassinated by the IRA.
Jack Royston is chief royal correspondent for Newsweek, based in London. You can find him on Twitter at @jack_royston and read his stories on Newsweek's The Royals Facebook page.
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