The Duke of Cambridge and Prince Harry have spoken of their enduring regret over their last conversation with their mother, disclosing they had been desperate to rush off the telephone and get back to playing instead.

The Duke and Prince, who were 15 and 12 when Diana, Princess of Wales, died in a car crash, said they had been busy at Balmoral when she called them, and had no notion that the short phone call would be their last.

The conversation, the Duke said, still weighs on his mind “quite, quite heavily”, while Prince Harry admitted he would regret it for the rest of his life.

The brothers spoke as part of a one-off documentary for television, in which they detail their warm memories of their fun-loving mother.