EXCLUSIVE: 'American Idol' Originals React to Simon Cowell's Surprise Finale Appearance

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It wouldn’t have been right to celebrate the series finale of American Idol without a visit from the show’s most infamous judge, Simon Cowell. But most of the original stars and host Ryan Seacrest didn’t think it would happen.

During Thursday night’s two-hour show, OG judges Randy Jackson and Paula Abdul took the stage to thank the fans and informed them that Cowell could not make it. But just moments later the opinionated Brit took to the stage, surprising them all.

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ET’s Sophie Schillaci caught up with Seacrest and former judges Randy Jackson and Paula Abdul after the emotional show, where they talked about Cowell’s appearance. Both Seacrest and Jackson insisted they were shocked by his big reveal.

“You know, I heard the crowd, and then I have a monitor in front of me so I could make out his pace,” the longtime host said. “I was like, ‘Oh my God that's him!’ He doesn't bend his knee when he walks. Like that has to be him! So I thought that was a great moment.”

Jackson agreed, telling ET, “We did not think he would make it. We really didn't. And it was like, wow and for all of us to be back together on that stage. Dude, come on.”

MORE: ‘American Idol’ Winners: Where Are They Now?

But no one fooled Cowell’s longtime frienemy, Abdul.

“As if he'd miss a moment like this!” she said (hopefully, pun intended). “I mean it didn't matter what anyone saying, yeah right. And I go Randy, and we're both going, ‘Yeah right!’”

The pop legend reflected on the impact of Idol and her time on the show, which ran for 15 seasons.

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“To have been a part [of it] from day one and help build an amazing legacy that changed the trajectory of everyone's lives, made dreams come true-- that we helped produce superstars… I'll always miss the entire process,” she said. “And, of course, the wonderful people along the way; even the annoying ones that have an accent that they start S-- and end with an 'imon.'”

Hmm, who could she be talking about?

Cowell’s return was one of many special moments during Idol’s last call.

“Tonight was really special for so many reasons. All the contestants who came back and then seeing Trent and his emotion,” Seacrest added to ET of winner, Trent Harmon. “That to me is what the show is. It's that raw, special emotion from the contestants.”

After his appearance, Cowell tweeted, “Hello. Idol bought back so many fun memories tonight. And we couldn’t have done it without the fans. Thank you.”