Daily Mirror's royal editor Russell Myers explained the toy had been given to Charlotte, as she's said to be a fan of the kids TV show.
"I’m told Princess Charlotte is a big fan of the Clangers so Prince William was presented with a little Clangers toy."
Adding that Prince William admitted he'd "dropped a few clangers in his time" upon receiving the thoughtful present.
Earlier this month, Princess Charlotte attended her first day of school, at Thomas's Battersea.
The Cambridge's middle child was dropped off by her mum Kate Middleton, and dad William, along with her brother, Prince George.
George, who is six, started at the school in September 2017.