Can you hear British accent? What is the Prince saying?

He says “how do you know I’m not a radio station.” Yes he is laughing the prank off. Then he says he is very proud to be a grandfather.

Yip, he mumbled a bit…but that is what he said!

Yes, that’s what he said and yes he was laughing it off.

I agree with @chyna

The middle sounded a bit like Charlie Brown’s Teacher

What @chyna said.

That part I can’t make out is ”....., so that is spelndid.” What is splendid?

“Very nice at being a grandfather at my old age if I might say so, so that is splendid.”

If what he is doing is approving the prank, I don’t believe it has any relevance anyway. And I don’t think he is approving or not approving of it. I would expect them to give superficial responses like that to most “reporters” or reporters otherwise he would waste all his time giving thought out answers.