This Morning's Phillip Schofield and Holly Willoughby were forced to apologise when Miriam Margolyes delivered a four-letter outburst live on air.
The pair gasped audibly as the Call The Midwife star described herself as a "t***" while recalling how she embarrassed herself in front of the Queen.
Holly and Phil promptly apologised to viewers, although Margolyes did not appear to notice their shocked reactions.
Describing her encounter with the Queen, she said: "Well, I have talked about this before on television, and I feel awkward saying it again.
"But I was invited to the palace as part of British Book Week and when the Queen came over to me, and she asked me what I did...in a very nice way, you know.
"And I said, like a t***, I'm the best reader of stories in the whole world."
Margolyes recalled how the Queen rolled her eyes and moved on to the next person waiting in line, a man who taught dyslexic children to read.
Impersonating the teacher, she said: "Ma'am, we've noticed that if you put the letters in different colours and the pages are printed in different colours, it helps the children absorb the information more quickly."
She said she had interrupted the pair's conversation, saying: "And I said, 'Really? That's fascinating, I didn't know that.'
"And she turned to me and went, 'Be quiet'. She had every right to do it but it was a bit discombobulating."
It is not the first time Margolyes, best known for playing Professor Sprout in the Harry Potter films, has sworn live on air.
In January last year, she uttered the F-word on the Peston On Sunday show, while regaling an anecdote involving Hollywood star Warren Beatty.
The swearword left the studio guests - Tory MP Sarah Wollaston and Lord Adonis - giggling, while Robert Peston was forced to apologise.
