The Duke and Duchess of Cambridge were among the first royals to send public wishes to the Duke of Edinburgh on his 99th birthday on Wednesday. Prince William and Kate shared photos of themselves with Prince Philip on their social media account, with the caption, "Wishing a very happy 99th Birthday to The Duke of Edinburgh!"
READ: Prince Philip is the third longest-living British royal - but who holds the record?
The Duke has a close bond with his grandchildren, particularly William and Harry, who he is said to have taken under his wing after the death of their mother, Diana, Princess of Wales in 1997. The Princes have followed in their grandpa's footsteps with their military careers and share a love of sport, including polo. Prince William also once described his grandfather as a "legend," to The Crown's Matt Smith, who asked him for tips on playing the Duke in the Netflix drama.
WATCH: Prince Philip's life in pictures
Philip lived with his uncle Louis Mountbatten, 1st Earl Mountbatten of Burma for several years as a young man and Lord Mountbatten also had a close relationship with Prince Charles. William appeared to pay tribute to Philip's uncle when he named his first son George Alexander Louis, and then named his second son Louis as well.
MORE: How Prince Philip became the rock of the royal family and its ultimate poster boy
© Photo: Getty ImagesThe Queen and Philip on the balcony on William and Kate's wedding day in 2011
William has also publicly admired the relationship of his grandparents, who celebrated their 70th wedding anniversary in 2017. During a BBC documentary about the Queen and the Duke, William said: "I'd love to know their secret. I think it’s fantastic and I’ve regularly asked them both how they’ve managed it, because they are the most lovely couple."
Philip retired from royal duties, aged 96, in August 2017 but has publicly attended the weddings of his grandchildren, including the more recent nuptials of Prince Harry and Meghan Markle, and Princess Eugenie and Jack Brooksbank.
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