Katy Perry has shown off her curves in a see-through lace dress at the American Idol after-partyCredit: BackGrid

The Teenage Dream singer, 38, flashed her underwear in the revealing garmentCredit: BackGrid

Katy revealed her black leather thong underneath the sheer dress, which she teamed with black lace-up heels.

The American Idol judge finished off her look with a chunky black ring and matching earrings.

She styled her hair in glossy waves and framed her features with shimmery eyeshadow and taupe lipstick.

Katy made an outfit change for the after-party, having worn a shimmering orange cut-out dress for the finale hours earlier.

Viewers were divided over the 𝑠e𝑥y garment, with some claiming it was unflattering and looked like a swimsuit.

One Twitter user wrote simply: “That dress is not flattering on Katy Perry!”

Another tweeted: “Is she at a swim meet?”

Katy also made headlines during the finale when she broke down crying over the contestants’ final performances.

Katy styled her hair in glossy waves and framed her features with shimmery eyeshadow and taupe lipstickCredit: BackGrid

The Idol judge finished off her look with a chunky black ring and matching earringsCredit: BackGrid

Iam Tongi performed early in the night, delivering a heartfelt rendition of Keith Urban’s song Making Memories of Us.

Before taking the American Idol stage, Iam met with Keith to chat about his song choice and get some pointers ahead of his performance.

He revealed early on in their discussion that his late father used to play one of the Australian country singer’s songs in their home when he was a kid.

Keith noted his “emotional connection” to the song, suggesting that it was the right choice for him.

Iam took the stage with his guitar strapped on and flip-flops on his feet.

He delivered a characteristically moving performance that left more than a few of the judges emotional.

Katy Perry was seen crying in her seat while Lionel Richie and Luke Bryan hid their feelings a little better.

After Iam was done singing, Katy opened the judging with this: “Can I just say one thing?

“In between you and Megan [Danielle] I had to grab a little tissue and fold it into a triangle because every time you come on and you sing the vibration that comes out of your mouth, it goes through the weeds of people’s hearts and it just gets to them.”

She concluded: “It moves us so much. So when you sing, I am ready to feel, baby.”

Luke Bryan and Lionel Richie both revealed that they, too, had been close to tears during the performance.

Katy and Luke cried again when he took the stage for a second time on Sunday.

Katy wore a glittery orange cut-out dress to the finaleCredit: Getty

Critics claimed it looked like she was wearing a swimsuit (seen with Idol host Ryan Seacrest, winner Iam Tongi and fellow judges Lionel Richie and Luke Bryan)