Prince William and Kate Middleton are planning a joint party to celebrate their 40th birthdays

Aww...

Prince William celebrated his 40th birthday yesterday, with the royal family sharing sweet tributes and photos on social media to mark the occasion.

The Duke of Cambridge decided not to release any birthday portraits, instead using his Instagram account to raise awareness for homelessness following his undercover charity work for The Big Issue earlier this month.

While William is said to have kept things low-key this week, choosing to spend the day with Kate Middleton and his three little ones, Prince George, Princess Charlotte and Prince Louis, the Cambridges are reportedly planning to host a joint birthday party later in the year.

Kate already reached the milestone birthday in January this year and threw a small intimate party at the couple's Norfolk residence, Anmer Hall.

Therefore William and Kate have decided that they'll mark their 40th birthdays together with a joint party, and the Queen is offering up one of her estates to host the bash.

Party at the palace, round two? Yes, please. 

Royal sources say that the Duke and Duchess should 'celebrate their landmark birthdays in style.'

The pair plan to celebrate at either Sandringham Castle or Windsor Castle later this year but the Queen will not confirm her attendance until the day, likely due to her ongoing mobility issues. 

Sandringham Castle is where the Queen chose to spend her 96th birthday, for a heartbreaking reason. HRH wished to spend her big day there, as it is where she feels closest to late husband, Prince Phillip.

Windsor Castle is also popular venue for a big royal party, as William’s 18th, Princess Anne’s 50th, Princess Margaret’s 70th and Prince Andrew’s 40th were all celebrated there.

With the Cambridge's set to leave London very soon, a big birthday bash could be exactly what they need for their introduction to life in Windsor!