Actress Martine McCutcheon claims she was once caught using the "royal loo" - by the Queen herself.
The former EastEnders star said she did not know whether to "curtsey or rush off" and said the Queen "didn't look very impressed".
Martine said the incident took place at a polo match in 2005.
She told the Sunday Mirror's Notebook magazine: "We were at the polo and due to meet the Queen when I suddenly needed a wee.
"I asked the Queen's butler where the nearest loo was and he said, 'It's down there, but you're not really meant to use that one as it's meant to be for Her Majesty. It's the royal loo but she's not due here yet so it's fine, go and use that'.
"So I heard someone knocking on the door and I was going, 'One minute, one minute', and I came out and it was the Queen with her assistant.
"She didn't look very impressed and I didn't know whether to curtsey or rush off.
"The assistant looked at me as if to say, 'Just go', so I ran off.
"So I'm one of the few people to have used the Queen's loo."