Prince William said that he once almost killed his cousin Zara Phillips while playing on the grounds of Balmoral. He and his brother, Prince Harry, stayed at Balmoral after their mother Princess Diana’s death in 1997. The brothers used to stay at the castle in Aberdeenshire in Scotland, along with their grandparents Queen Elizabeth II and her husband Prince Philip.

The 33-year-old royal recounted a time when he and his cousins, Peter Phillips and Zara, were playing on the grounds of the castle. He told how he and Peter got into trouble after riding a quad bike at Balmoral. William was speaking to Sky News for a special documentary “Our Queen at 90” in honor of Elizabeth’s 90th birthday Thursday.

“We were chasing Zara around who was on a go-cart, and Peter and I managed to herd Zara into a lamppost. And the lamppost came down and nearly squashed her, and I remember my grandmother being the first person out at Balmoral running across the lawn in her kilt,” William reportedly said. He recounted how his grandmother was furious at them.

William also opened up about the queen’s presence in his life as a “strong female influence” after he lost his mother at a young age.

William said that at that age he needed someone like his grandmother to look up to. He added that she understood the complexities of losing a loved one.