Prince Philip's son Prince Charles and grandson Prince William are among those who sent birthday messages to the royal, who has turned 99.
The prince turned 99 on Wednesday and his grandson, Prince William, and his wife Duchess Catherine, each shared a photo of themself with the veteran royal, alongside the official portrait of Philip and his wife Queen Elizabeth, which has been released to mark the occasion.
William and Catherine wrote on their Instagram account: "Wishing a very happy 99th Birthday to The Duke of Edinburgh!"
Philip's eldest son, Prince Charles, also sent a birthday message through his Instagram account.
The message was accompanied by a photo of the princes on a boat when Charles was a boy, and another of them years later, as well as the official image.
The caption read: "Wishing The Duke of Edinburgh a very happy 99th birthday!"
A post on the Royal Family official Instagram account shared a selection of archive photos of Philip, as well as a more recent one of him being given a gift by the queen.
It was captioned: "Wishing The Duke of Edinburgh a very happy birthday!
"His Royal Highness turns 99 today and will spend the day with The Queen at Windsor."
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A post shared by The Royal Family(@theroyalfamily) on Jun 10, 2020 at 1:26am PDT
It was previously claimed Philip will be marking his birthday with a quiet lunch with his wife.
A source said: "He's not one for fuss, as you know."
His cousin and childhood friend, Lady Myra Butter admitted Philip has always insisted on "no fuss, no bother".
She said: "The secret is that he just does everything he has previously done, but slower.
"He still enjoys the greatest role of all, supporting the Queen. As for a party to celebrate turning 99? Goodness me, no! He never wants a fuss, ever!"
Lady Butter described Philip as "an enigma" and praised him for maintaining a "thirst for knowledge" even as he grows older and frailer.
He said: "He has such an incredibly active mind. And he's a great reader, so interested in things.
"He's got enormous knowledge and I am absolutely certain there must be a link between that and his long and healthy life. He's such an enigma, really.
"He has that thirst for knowledge. He still paints, he sees his horses and keeps abreast of everything in the news."