There is an interview with Brian Cox in the Guardian today that is gaining a certain amount of traction. You can see it on https://www.theguardian.com/tv-and-radio/2020/jan/13/successions-brian-cox-i-was-touched-up-by-princess-margaret.
Here's the money quote:
“I was at the Royal Court. I was doing a play with Alan Bates and it was my 23rd birthday and I’d been given a red shirt from Lindsay Anderson. I’d just washed my hair so I was sort of glistening, heh heh heh, and I walked in and was introduced to her. She put her fingers on my shirt, and said: ‘This is a lovely shirt.’ And she started to run her fingers down the inside of my shirt. And I went: Uh oh! What do you do when you’re being touched up by a royal?”
What do you do?
“It was so funny. James Bolam, he could see what was going on and started going ‘Ooooh’ out of the side of his mouth, which somehow said princess didn’t take in at all. She just kept saying: ‘You were so wonderfully hooded on stage. I wanted to know more about you …’ She was an extraordinay creature. I excused myself and said: ‘Thank you, ma’am,’ and it came to a natural end.”That would have been in PG's tenure as a Royal Court assistant director unless I miss my guess.