The Oscar-winning actress appeared on the BBC Breakfast show, which airs between 6am and 9.15am local time, and let slip a four-letter word as she discussed her admiration for famed English thespian Sir John Gielgud.
Mirren paid tribute to the late actor and told of her love for his clipped accent, even when using curse words - before stunning presenters by uttering an obscenity.
She said, "He was always my inspiration for the choices he made, he was this great knight of the British theatre... that always inspired me. He always took such edgy choices, (and he would always say) in that wonderful voice he had, 'You little s**t'."
When the presenters pointed out her slip, Mirren clasped a hand over her mouth and laughed, adding, "Oops, I'm so sorry."
Presenter Bill Turnbull then told viewers, "That never happened. If you heard that, we are very sorry."