Reddit mentions of The Housekeeper's Diary: Charles and Diana Before the Breakup

>The chances of that actually happening are slim. The chances of it being reported if it did happen are next to zero.

Former servants make money by publishing tell alls.

edit: to add examples because apparently 203048154 does not understand how to use google.

example 1

example 2 info from a court case involving a servant

example 3 - a book written with benefit from interview with servants

It was in more than one of the biographies I've read about her.

Edit: And In The Housekeeper's Diary: Charles And Diana Before The Break-Up, author Wendy Berry describes what's textbook BPD behavior in Diana: Splitting staff members black/white, screaming at her husband one minute and then wanting a hug the next, going into absolute ragefits when she can't find the hairbrush she wants, parentifying both of her children (but especially William), etc. etc.. Far from being the narcissistic sociopath that Diana tried to paint him, Charles instead comes across as a bit self-centered and clueless but generally well-meaning. Berry describes Diana just screaming at him and him basically wringing his hands and saying, "But Darling, what have I done?".

So there's that, too.