The Duke of Sussex was spotted driving his pregnant wife to the birthday celebration after Prince Charles celebrated his big day by meeting 70 inspirational people also marking their 70th this year.
The Duke of Cambridge drove separately with his wife, Kate.
Getty's photographer Chris Jackson released a photo of Charles and Camilla inside the big bash.
The couple looked glam as they smiled energetically.
"On his 70th Birthday The Prince of Wales poses for a photograph with the Duchess of Cornwall before heading to his birthday party at Buckingham Palace tonight," Jackson wrote.
On November 14, the day of Charles' 70th, the Royal Family celebrated the future monarch by releasing two new portraits.
The pictures were taken by Chris Jackson in the garden at Clarence House in September 2018.
The Royal Family also released a video montage to their official Twitter page.