Sofia Richie and Elliot Grainge Are Engaged! Nicole Richie, Evan Ross and More Celebrities React

“American Idol” celebrated its 20th birthday in style Monday night.

Katy Perry is flipping over the latest "American Idol" season.The pop star took a fall on the "Idol" set while dressed as "The Little Mermaid" on Sunday's episode. Video of the incident shows Katy kicking her feet up on the judge's table while Ryan Seacrest talks. Suddenly, as Ryan reacted to a loud bang, the camera panned to Katy, who was on the ground after tumbling off her chair. "Oh!" Ryan said while running over to Katy, her mermaid tail kicking up into the air.

Katy Perry knows what she’s doing as a judge on American Idol. She just doesn’t know how to do it while wearing a mermaid costume!!

Katy Perry almost ended up “under the seat” during the latest episode of “American Idol”.

Lionel Richie has spoken! And the American Idol judge is markedly less judgmental when it comes to his baby girl’s new man!

judges Paula Abdul and Randy Jackson are reuniting for the singing competition's landmark 20th season. They are returning to the judges' table for the special reunion episode airing Monday, May 2, and only ET has the exclusive first look at the duo back in action.Abdul and Jackson served as Idol judges together for the franchise's first eight seasons, from 2002 to 2009.

Future father-in-law! Lionel Richie couldn’t be happier for his daughter Sofia Richie following her engagement to Elliot Grainge.

Lionel Richie shared his thoughts on his daughter Sofia Richie's engagement to music executive Elliot Grainge, and he couldn't be more ecstatic.MORE: Sofia Richie's $300k engagement ring is mighty like father Lionel Richie'sSpeaking to American Idol red carpet, the musician initially joked: "It was a slippery slope there for a moment, as with all families."VIDEO: Lionel Richie performs All Night Long in New York throwbackHe then added: "I love Elliot, I've known him since he was 12, so it was one of those things where I don't have to go back and check out the kid, I know who he is. "They're so happy. As a papa, as a dad, that's my little girl.

Some friendly advice. Katy Perry had a hilarious reaction when an American Idol contestant sang a track by her ex-boyfriend John Mayer — and she offered him a tip he could use in the future.

Katy Perry has often had moments of hilarity on American Idol, but on the show's latest episode, an unexpected moment ended up a little more awkward for her than expected.MORE: Katy Perry leaves viewers stunned in whimsical green pantsuit live on American IdolThe latest live episode of the show on Monday night featured the Judge's Song Contest, a segment where each contestant was anonymously given a song chosen by the judges and the song they'd perform would net that judge a point.VIDEO: Katy Perry's husband Orlando Bloom cuts a turkey on ThanksgivingFor contestant Noah Thompson, he was given a choice of three songs, two of which ended up being by John Mayer and one by John Denver.While he initially leaned toward the John Denver song, he ended up opting for the John Mayer track Heartbreak Warfare, delivering a performance that impressed the judges.MORE: Katy Perry updates fans with baby number two newsHowever, the moment quickly turned slightly uncomfortable when Ryan Seacrest asked Noah who he thought chose the song, and he picked Katy, unaware of her history with the singer-songwriter, having been in an on-and-off relationship with him.She quickly tried to figure out how to react as the audience let out a few knowing chuckles.

Not for everyone? After winning over the judges — and viewers at home — Kenedi Anderson, Wyatt Pike and more contestants have dropped out of American Idol for various reasons over the years.

American Idol judges Luke Bryan and Lionel Richie had a hilarious moment on the show's latest installment, puncturing an emotional moment with a comedic one.MORE: Lionel Richie left in tears by emotional American Idol auditionThe country star seemed to have quite the strong reaction to contestant Leah Marlene's performance on the new live episode on Sunday night.VIDEO: Luke Bryan calls on fans to help him after ‘losing money’ in Las VegasFollowing her incredible routine, the judges praised her for her transformation over the course of the competition, with Luke in particular glowing with pride."The beauty of this show and why it works year after year is watching what is happening to you right now," he said to Leah.MORE: Katy Perry talks disagreements with American Idol judges Luke Bryan and Lionel Richie"It's really emotional for me and us to watch you grow and come out of your deal.

Can you believe it has been 20 years since American Idol premiered?!

HunterGirl did it again, moving forward into the next round of “American Idol” and celebrated with a Miranda Lambert cover.