OCC: if he still was married to Diana she'd out him in a heart beat when the marriage was going side ways.
I reckon she might refrain from outing Charles for the sake of the children. Doesn't matter how cool we think she was with cultural matters, she was a woman of a certain (upper)middle class cohort--young enough to benefit from the sexual revolution and feminism, but a tad too old to automatically believe that society at large was progressively liberal on GLBT issues. F'rinstance, a quick Internet search shows she never made any noises about supporting gay marriage.
And IIRC she was pretty oblique when referring to the female CPB during the famous Martin Bashir interview.
OOC: Paul Newman is dead. He was bisexual.
Even now I'm still asking myself, "How can Paul Newman be dead?"
But I do think the public record of his sexuality is still pretty sketchy, and it's not like he wasn't a star for half a century. Though of course he wasn't an heir to the royal thrown, but still. These things can be hidden by the famous.