“I was delighted by that," said Ferdinand, 44. "He was a bit out of order, if I must be honest.
“Aston Villa, his team he supports, beat Man United at the weekend and that was the first thing he said.
“But, no, it was great. It was great to see him. I’ve been lucky to meet him quite a few times, so talking about family really.
“How your family are doing, how mine are doing and I was just … no matter how many times you meet someone of that stature, you walk in and your knees are buckling all over the place and nervous.
“Yeah, definitely. It’s the future king, man. It’s Prince William, man, there’s levels.”
Ferdinand was joined at Windsor Castle by his wife Kate and father Julian.
He won a Bafta and plaudits for hosting BBC documentary Rio Ferdinand: Being Mum and Dad about coping with the loss of his former wife Rebecca in 2015 to breast cancer and looking after their three children.