Not according to two books by different authors I've read. It's said in both of them, that's the official line to throw people off the scent and keep the truth hidden, but Di and JH were alleged to have been bumping uglies way
before Harry was born.
Also, let's not forget the fact that the old baked bean stepped in at the 11th hour at Burrell's trial, causing it to collapse by suddenly 'remembering' she had
given him permission to keep the items belonging to Diana for which he was up in the dock charged with stealing. Although she didn't 'remember' until halfway through the trial, which just happened to be the night before he was due to take the stand and give his
evidence. Funny that.
Those of a cynical, or at least, questioning nature might wonder if she rather belatedly got him off the hook to prevent him blurting out something she'd rather the GBP never found out.... and I don't mean him letting it slip that she likes a couple of Jammie Dodgers with her cup of Earl Grey.
Harry's parentage wasn't the only revelation in those books either ~ there were plenty more regarding many members of Buck House, some of them going back years. Both books were a very enlightening read. If anyone's interested, please PM me and I'll give you the titles and authors names.
Anyway, back on topic ~ Bertie for a boy, Gertie for a girl.