Joined by her fellow judges Luke Bryan and Lionel Richie, the trio announced the exciting development in a segment that appeared to have been taped recently -- likely after they'd already filmed the audition rounds.
"I can't tell you how excited I am that we're going to have a fourth judge on the show this year," Richie said with a smile, before anyone had actually revealed the baby news.
"I think it's a perfect addition to this panel," Bryan added, before asking Perry to reveal the identity of the so-called "fourth judge"
"We're having a baby!" Perry declared, rubbing both hands over her baby bump.
As she got a celebratory hug from Bryan and Richie, Perry laughingly declared, "Oh my god, I'm terrified!"
Her Idol co-stars and friends were gleeful and effusive in their support, but Bryan still made sure to poke fun.
"Does this mean your dressing room gets bigger?" Bryan jokingly asked.
"Well, I'm definitely gonna get fat," Perry said with a laugh. "So look forward to that! Everything is going to get bigger and better on American Idol season 3!"
Perry, Richie and Bryan all addressed the news on Twitter as well.
Perry wrote some kind words about her co-stars, and the roles they will play in her baby's life, writing, "Can’t wait for Uncle @LionelRichie and Uncle @LukeBryanOnline to teach my kid how to shop til they drop, and then tie a fishing hook 👶🏻 😜."
Meanwhile, Richie and Bryan both congratulated Perry and her fiance, Orlando Bloom. Richie wrote, "So exciting! Congrats to Katy & Orlando. So much love." Bryan tweeted, "Congrats @katyperry and Orlando Bloom! We’re looking forward to adding a 4th judge to the family."
After the video dropped, she confirmed the news in an Instagram Live session, where she also revealed that she is due in the summer.
On Sunday, Perry celebrated International Women's Day with a performance at the Women's Cricket World Cup Final in Melbourne, Australia, and revealed that she hopes she'll be having a baby girl with Bloom -- who is already dad to a son, 9-year-old Flynn, whom he shares with ex-wife Miranda Kerr.
"I hope it's a girl," Perry confessed during her song, "Wide Awake," while pointing to her burgeoning baby bump. The crowd quickly erupted in screams, with Perry letting out a huge smile and continuing with her performance.
Hours before the start of the Women's Cricket World Cup Final on Saturday, Bloom fawned over his ladylove in a sweet Instagram post. The expectant father shared a beautiful photo of Perry in a dress that showed off her baby bump, and wrote in the caption, "My babies blooming ❤️."
Check out the video below to hear more from Perry about her pregnancy and her plans for motherhood.
American Idol airs Sundays at 8 p.m. ET/PT on ABC.