Prince William and Prince Harry. Picture: Bang Showbiz

Prince Harry will "regret for the rest of his life" how quick his last phone call with his late mother Princess Diana was.

The flame-haired royal tragically lost his mother in August 1997 when he was just 12 and he deeply regrets the last conversation they had because he was desperate to get off the phone so he could go back and play with his brother Prince William whilst they were spending time with their father Prince Charles at Balmoral.

Harry said: "As a kid I never enjoyed speaking to my parents on the phone. And we spent far too much time speaking on the phone rather than speaking to each other, because of the way the situation was. And the phone rang and off he [William] went to go and speak to her sort of for five minutes ...

"I can't really necessarily remember what I said, but all I do remember is probably, you know, regretting for the rest of my life how short the phone call was."

And Prince William, who was just 15 at the time, wishes he wouldn't have been so "blasé" about the call.

Speaking for the Diana, Our Mother: Her Life and Legacy documentary, Prince William added: "At the time Harry and I were running around minding our own business, you know, playing with our cousins and having a very good time ... I think Harry and I were just in a desperate rush to say goodbye, you know, see you later and we're going to go off. If I'd known now obviously what was going to happen, I wouldn't have been so blasé about it and everything else. But that phone call sticks in my mind quite, quite heavily."