The Duke and Duchess have both turned 40 this year, and they will be celebrating it with a joint birthday party later in the year.
William is holding off on any major celebrations for now and instead, he and his wife - whose birthday plans in January were affected by the coronavirus pandemic - will join forces for a bigger bash towards the end of the summer.
The pair plan to follow tradition to "celebrate their landmark birthdays in style" by collaborating on their celebrations and have been given the go-ahead to invite people to either Windsor Castle or the Sandringham Estate for the function.
However, according to the Daily Mirror newspaper, The Queen won't confirm if she'll be joining her family at the party until the day of the bash because of her ongoing mobility issues.
When Catherine turned 40 earlier this year, she had an intimate celebration with friends and family at her Anmer Hall home in Norfolk amid concerns about the Omicron variant of coronavirus.
At the time, a source said: "There are likely to be low-key celebrations for the Duchess. She didn't want anything flashy anyway – that's not exactly her thing – but particularly given the current climate anything is likely to be scaled down."
A similar big party was staged in Windsor in June 2000, when William turned 18, Prince Andrew turned 40, Princess Anne turned 50, and the late Princess Margaret turned 70.