Prince Charles thought Gemma Arterton was "common".
The 33-year-old actress - who grew up in Gravesend in Kent, South East England - feels "sad" that her natural accent has softened but she saw the funny side when she realised the prince expected she'd need a lot of work to practice adopting an aristocratic tone.
She said: "I've met Prince Charles a few times and he's really lovely, such a nice man.
"He came to see me in 'Nell Gwynn', which is interesting, because she's a proper Cockney who became aristocracy.
"Then I saw him again and he said, 'How's your accent coming on? Are you working on it?' I thought, 'You think I'm so common!'
"My Cockney accent is practically gone now and I do feel sad about that - a bit fake maybe. When I'm around my family, they sound so different to me."
Gemma lost her accent when she attended drama school.
She recalled: "Before that, I didn't care what people thought of me - I ate what I wanted, spoke when I wanted.
"Then I got to the school and someone told me to try not talking because it would create more mystique.
"So I'd go up to the canteen and just sit there, eating my lunch in silence."
But the 'King's Man' actress - who had a scholarship for drama school - thinks the industry is changing and becoming more accepting of different backgrounds.
She told Britain's Harper's Bazaar magazine: "I think it's different now. In those days, if you had a regional accent, you'd probably only get cast as the funny part in a Shakespeare play - now you could play Rosalind in 'As You Like It' with a northern accent. It's changed a lot."