How does a royal family member celebrate their birthday?
Well, when it comes to the Duchess of Cambridge, the understated royal opted for a low-key day - but that's not to say there wasn't some cake involved!
According to Vanity Fair, Duchess Catherine rung in her 37th year with an intimate tea party at Kensington Palace surrounded by her family.
"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," an insider told the publication's royal reporter Katie Nicholl.
Vanity Fair also reveal the mother-of-three spent her birthday at her Kensington Palace home with her two youngest children Prince Louis, eight months, and Princess Charlotte, three, while five-year-old Prince George was at school and Prince William attended an official engagement visiting the Air Ambulance service in London to mark their 30th anniversary.
WATCH: Prince William reveals Prince Louis is teething. Post continues after the video...
At the event, William was announced as the organisation's new patron and the proud husband joked to well-wishers that he most certainly hadn't forgotten his wife's birthday.
When a group of children gave the Duke of Cambridge a birthday card to pass onto his wife, William reportedly mused: "Well done for remembering!"
Before sweetly adding: "I did remember this morning, so that was okay!"
Royal reporter Rebecca English, who attended the event, shared a snap of Kate's card and the adorable message written inside it which read: "Kate I hope you've had the best birthday you could ever imagine."
And it wasn't just birthday cards William was given!
At the event, the royal was also inundated with gifts for his three children, including a toy helicopter.
"Look at these, they are amazing! That will go down very well. Louis will be chewing that before long," Prince William revealed of his eight-month-old son, who would no doubt love munching on the toy to help with teething.
Before adding that his helicopter-mad older son George would also be thrilled.
"I couldn't go back without a toy helicopter. George would never forgive me," he joked.
There's no doubt that after his engagement, William headed back home to spend the rest of the day with birthday girl Kate.