Media mogul Simon Cowell has thanked Kelly Clarkson for standing in for him on America's Got Talent while he recovers from back surgery. 

Cowell underwent six hours of surgery at the weekend following a fall from a new electric bike he was testing at his house in Malibu.

The 60-year-old was taken to hospital where he had an operation on Saturday night, which involved a number of procedures including having a metal rod put in his back.

Clarkson is filling in as a judge on the reality TV talent show in the US while Cowell recovers and joked on Twitter that he should not "hurry back" as she is "getting pretty comfortable in your chair".

"I'm just kidding, get well," she said.

Simon Cowell and Kelly Clarkson
Simon Cowell and Kelly Clarkson have been good friends since she was the first winner of American Idol in 2002

Cowell tweeted after the show: "Thank you Kelly Clarkson. Miss all of you. What a great show."

Clarkson shared the news she would be filling in with a spoof "urgent memo" that she shared on Instagram at the beginning of the week.

"My friend, Simon Cowell, is doing better now but was in an accident and won't be able to make Tuesday and Wednesday's live shows for AGT, but no worries America, someone far wiser, cooler and hotter is taking his seat!" she quipped.

"The unbelievably amazing Kelly Clarkson. You're welcome in advance."

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