I’ve never heard that rumour, but if there’s any source for it it’s probably noted in the end notes/foot notes.
I went through the index, and I couldn't find any mention of the source. The names credited to Page 120 are Edward Adeane (Private Secretary to the Prince of Wales from 1979 to 1985), Barbara Barnes (the princes' nanny), Stephen Barry (valet to Prince Charles), Michael Colborne (private secretary to Prince Charles), and Oliver Everett (private secretary).