The Duke of Edinburgh celebrates his 99th birthday today and he received messages from well-wishers all over the world. One sweet and heartwarming message came from his grandson Prince William and his wife Duchess Catherine, who posted some amazing pictures on their official Twitter account.

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Prince William & Duchess Kate's sweet birthday message

The Duke has a close bond with his grandchildren, in particular Prince William and Prince Harry, whom he reportedly took under his wing after the tragic death of Princess Diana in 1997. The caption of William and Kate's tweet read "Wishing a very happy 99th Birthday to His Royal Highness The Duke of Edinburgh!"

Prince William actually described his grandfather as an "absolute legend" when he was asked about him by actor Matt Smith, who played the Duke of Edinburgh in the first and second seasons of the popular Netflix series The Crown.