Story highlights Prince William says he was in a hurry to get off the phone to go play

"I do remember ... regretting for the rest of my life how short the phone call was," Harry says

(CNN) Prince William and Prince Harry have spoken of their regret at the brevity of their final phone call with their mother, Princess Diana, just hours before her 1997 death in a car crash in Paris.

In a new documentary set to release on Monday by ITV in Great Britain and HBO in the United States, Prince Harry recalls how quickly he got off the phone with his mother.

The two brothers were at Balmoral Castle in Scotland when Diana called from Paris.

"I can't necessarily remember what I said, but all I do remember is regretting for the rest of my life how short the phone call was," Harry told ITV.

Diana, Princess of Wales, on holiday with Prince Harry.

"If I'd known that that was the last time I was going to speak to my mother, the things I would have said to her," he said. "Looking back at it now -- it's incredibly hard. I have to deal with that for the rest of my life: not knowing that it was the last time I'd speak to my mum, how differently that conversation would have panned out if I'd had even the slightest inkling that her life was going to be taken that night."

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