Busker stunned after she asks Kelly Clarkson to sing unaware of who she is

It's always nice unexpectedly bumping into a celebrity, but it's probably even more of a rush singing alongside one without even realizing it.

And that's exactly what happened to one busker who was left totally stunned after she asked Grammy award-winning singer Kelly Clarkson to sing while completely unaware of who she was.

Clarkson, who was in Las Vegas ahead of her appearance at the iHeartRadio Music Festival on Saturday (23 September), joined the talented street performer on the sidewalk as she showed off her powerful pipes.

The Since U Been Gone singer boasts a whole array of accolades from her impressive decade-spanning career since she was crowned victor of the popular US television talent contest American Idol back in 2002.

However, that hasn't seemed to get to her head at all after she buddied up with the busker to perform for the Sin City crowd.

The 41-year-old has since taken to Instagram to share with her 7.1 million followers the incredible encounter.

In the short clip, Clarkson can be seen singing along to Tina Turner’s smash-hit What’s Love Got to Do With It, while the street performer danced and cheered on beside her.

At first, the woman supportively claps for Clarkson before finally realizing who she was, at which point she pointed at the world-famous singer and screamed before throwing her arms up and hugging her.

Clarkson captioned the video: "I was on my way to soundcheck for @iHeartRadio tonight in Vegas and was tipping this incredible woman killing some Tina Turner and then she asked me to sing and had no clue who I was, and then it hit her, and it made my day!"

The Kelly Clarkson Show host added: "She gives the best hugs and sings her tail off! See ya tonight Vegas!"

The wholesome moment has since clocked up more than 238k likes at the time of writing as well as thousands of comments from fans eager to share their reactions to the heartwarming clip.

One Instagram user penned: "This just put the biggest smile on my face. Protect these two at all costs."

"These are the best!" praised a second. "Love that you do this. So good for the soul!"

A third chimed in: "This is incredible. I can’t love this more! Seriously one of the realest and most talented celebrities! I would have died!"

"This is so adorable," gushed a fourth, "it really proves that you are kindest and most humble queen ever Kelly."

"And this is why you will forever be America's #1 American Idol," added a final Instagram user.