Speaking ahead of the day, a source told Vanity Fair: 'Kate's not into big birthday celebrations, but [Prince] George and [Princess] Charlotte adore birthday cake, so there will be a special tea party at the Palace with candles and presents'.
Prince William has spent his wife's birthday participating in training exercises at Royal London Hospital, flying with first responders in a rescue helicopter. But after a quiet day with baby Prince Louis, nine months, the mother of three was no doubt showered in gifts by her family.
The group gave William a card for his wife's birthday, which was made by a group of children, according to the U.K.'s Hello magazine.
When receiving the card, reporters captured him saying: "I did remember this morning, so I was OK".
George will be celebrating his sixth birthday in July, while baby Louis, turns one on April 23.
London's Air Ambulance account have said that staff are "so proud" to be celebrating the 30th anniversary of the service being founded with the Duke of Cambridge, the charity's medical director has said.
Amman in Jordan was home to Kate and her family for a few years in the mid 1980s, where she attended a nursery school from the age of three, before returning to Berkshire.
The 36-year-old worked as an air ambulance pilot from 2015-2017 with the East Anglian Air Ambulance.
Kate and Prince William have already birthed three children (George, Louis, and Charlotte) in a bid to crush Royal newcomer Meghan Markle's claim to mummy fame by springtime.
The couple joined Kate's parents, her brother James, and sister Pippa, to see a Cirque de Soleil show at the Royal Albert Hall in 2013.