The duke was at an investiture ceremony at Buckingham Palace where he told author Julia Donaldson of the upcoming celebrations.
Julia, a former Children’s Laureate, is perhaps best known for penning the classic children’s book The Gruffalo, which William said is favoured by the royal children.
“He said it's his daughter's birthday today and he loves the book,” the author revealed.
“He reads my stories to his children, and he said he was going to have quite a rowdy party – he's got a lot of children (coming).”
Princess Charlotte, who turned four on May 2, has had her latest milestone marked by members of the royal family, ahead of the expectedly anticipated birthday party.
Proud parents the Duke and Duchess of Cambridge released three adorable new snaps of their daughter ahead of her big day - much to delight of royal watchers.
Harry and Meghan also sent well wishes in the form of an Instagram comment, wishing their niece ‘lots of love’.
Princess Charlotte Elizabeth Diana of Cambridge was born on May 2, 2015, at 08:34am at the Lindo Wing at St Mary’s Hospital in Paddington.
She currently attends Willcocks Nursery School and is due to start the same primary school as her brother, Prince George, in September.