Prince William said Princess Charlotte is 'growing up fast' and 'tells anyone who asks that she is 16'.
Speaking on an engagement at an engineering firm in the West Midlands yesterday, William said another family was invited to celebrate his daughter's big day over the weekend.
Asked about Charlotte's celebrations, William said: "She had a lovely day thank you.
"Last year it was her birthday in lockdown but this year we were able to have one other family over.
"They grow up very fast. It was great fun."
Prince William later joked "if you ask her, she says she's 16... Charlotte says, 'I'm six now, I'll do what I want".
A photograph of Charlotte looking happy and relaxed in a floral summer dress was released to mark her sixth birthday on Sunday.
Charlotte's long hair is loose and tousled in the picture taken by her mother the Duchess of Cambridge.
The new photo was taken in warmer weather with the smiling princess pictured outdoors while wearing a dark blue short sleeved dress with a pink floral design.
The dress is £59 design from British children's clothing brand Rachel Riley.
The new image was not shared on the Cambridges' social media accounts after William said they were joining the sporting world for a four-day social media blackout to show that online abuse is not acceptable.
The relaxed look is a contrast from the photos which marked Charlotte's fifth birthday.
