Kelly Clarkson was mistaken for Carrie Underwood - and she went along with it

Speaking on her own talk show 'The Kelly Clarkson Show', she recalled: "This girl came up to me and was like, 'Oh my god, your song 'So Small' is one of my favourites. And I kept thinking, 'I don’t have a song 'So Small'. And then she said another song and I was like, 'Oh, you think I’m Carrie Underwood.' I look nothing like Carrie Underwood.

"I was so embarrassed for her that I just … She was like, ‘Can you sign this?’ And I totally signed ‘Carrie Underwood.’ I think that might be illegal!"

Meanwhile, Kelly previously revealed she loves being mistaken for Carrie.

She said: "That happens to me all the time! I have been asked all the time or they'll be like, 'Oh my gosh, I love your song 'So Small'. And I'm like, 'I don't even know what that is.' And then, I'll find out it's Carrie! I'm like, 'Thank you!' Cause I'm, like, legit 100 pounds heavier than Carrie."

Carrie and Kelly both won their series of 'American Idol' but the latter - who triumphed on the talent show in 2002 - previously confessed she felt "bitter" for years after winning the show.

The 38-year-old singer said: "The first three years of my career was me just paying for winning a talent show. I got real bitter. I was just looking for anyone to talk to who knew what I was going through. And that's why I like to do that for artists on 'The Voice'. It's actually healed that bitterness I used to carry, being able to be that for somebody else. It's really funny, because I knew that the winner of Idol would have to do that movie and I didn't want to do that movie. And I think Justin [Guarini; who was runner up] did.

"So, we were totally cool with him winning and me not winning, so I didn't have to do [the movie]. But I won, and had to do it. Contractually obligated."