Diana wanted to find out if he was the right man to work for her so she let him in on an incredible state secret – the sex of her baby.
By disclosing the bombshell information Diana was trying to establish whether Paul, who at the time was an aide to the Queen, could be trusted to keep his mouth shut.
He recalled: “Diana poached me. A few years before I worked for her, she tested the water at Balmoral when she was pregnant with Harry.
“She made a beeline for me and pushed me into the dining room. She shut the door and said, ‘Put your hand on my tummy, just there… You feel that? It’s a boy’.
“She was handing me my biggest test. I was petrified the news would break but I passed – she knew she could trust me.”
Paul also said how the Queen advised him to get married after he was caught up in a gay sex scandal on the yacht Britannia.
He said: “Her Majesty said, ‘Paul, the institution of marriage is a wonderful thing .”
Paul was married to Prince Philip’s maid Maria for 32 years but this week announced he was getting wed to his lawyer partner Graham Cooper in April.
Paul Burrell teases his exclusive interview this Monday