As a close confidante of the late People’s Princess, Fergie, 61, would have been privy to many of Diana’s secrets.
“They had their tiffs over the years, but Fergie was one of the few people Diana could turn to with delicate matters,” the insider continues. “Fergie swore to take many of Diana’s secrets to the grave – but Harry not being Charles’ kid is simply just not one of them.”
Not helping matters is the royal family’s stance of maintaining “a dignified silence on the matter” – which the insider says has “always bothered” royal rebel Fergie.
“Why not nip it in the bud?” ponders the source. “It’s an offensive rumour and it’s the last thing they all need right now, especially Charles.”
Now, Fergie is determined to publicly go into bat for Diana, arguing that the facts and timeline clearly speak for themselves.
“[Diana] hadn’t even met Hewitt when Harry was conceived [in 1984],” the source explains.
WATCH: Harry & William unveil the new Princess Diana statue (Article continues after video)
“It’s chronologically impossible for [Hewitt] to be the father. It’s all a silly conspiracy theory and she’s absolutely fed up with it. There’s absolutely no question that Charles is Harry’s father.”
Recently, Fergie lamented her sadness over not being a grandparent together with her friend.
Speaking to Bella magazine, she said: “We’d be having granny parties together and having a great time.”
For more, pick up a copy of New Idea. On sale now!