Prince Willaim turned 36. The staff of the Duke and Duchess of Cornwall marked the occasion by sharing a touching photo of Prince Charles holding William as a baby on Twitter and Instagram.
The black and white photo is part of a heart-warming set taken of Charles and Diana at Kensington Palace when their eldest son was just six months old.
The image was shared with the caption: 'Happy 36th Birthday to The Duke of Cambridge! #HappyBirthdayHRH,' alongside a recent one of Charles and William.
Kensington Palace, which handles matters related to the Duke and Duchess of Cambridge shared a photo of William looking dapper at a recent black tie event with the caption, ‘Happy birthday to The Duke of Cambridge! Thank you to everyone for their lovely messages #HappyBirthdayHRH.'
The Royal Family Instagram account shared a photo of William with his grandmother the Queen, 92, with a similar celebratory message.
William spent the day with Prime Minister Theresa May at the opening of the new Defence and National Rehabilitation Centre (DNRC) in Nottinghamshire.
The £300million centre, which was created thanks to the vision of the late 6th Duke of Westminster, was formally gifted to the nation by his son, the 7th Duke of Westminster, at a ceremony attended by the Duke of Cambridge and Mrs May.
The Duchess of Cambridge, 36, is currently on maternity leave following the birth of their third child, Prince Louis.
The mother-of-three is taking time off from royal engagements in order to spend time with her sons and Princess Charlotte, three.