Carrie Underwood "couldn't say no" to 'American Idol'

A source told DailyMail.com: "They have asked Carrie in the past to be a judge and either timing, money or other commitments have got in the way to make it a reality.

"She has been asked to coach on 'The Voice' as well, but it just never seemed right.

"Even with the opening she has to speak to the same people at NBC by working with 'Sunday Night Football', she has always felt that she needed to be loyal to 'American Idol'.

"She has always monitored the show that started her career, and now she couldn't say no."

Carrie hopes that her involvement will help to breathe new life into the show.

The insider explained: "Carrie feels she is the best star to have come from 'American Idol' and judging on the show to make another superstar will help cement her legacy with the show.

"She is looking forward to every joy she gets from giving back and is more than ready to make the show the monster show it once was."

Carrie is set to join Lionel Richie and Luke Bryan on the judging panel for season 23 of the show.

In an announcement video, Carrie - who won the fourth season of 'American Idol' back in 2005 - said: "I went from nobody knowing my name to tens of million of people watching the show.

"I'm proud of everything that I was able to accomplish on the show and I'm so proud of everything I've accomplished since."