'American Idol' Alums Reflect on Their Most Cringeworthy Moments and Reuniting for Season 20 (Exclusive)

ET spoke with some of the show's biggest past stars at the 20th anniversary reunion special on Monday.

American Idol brought together some of the show's brightest lights and most celebrated stars for Monday's "Great Idol Reunion" special, celebrating the show's 20-year history. ET was at the star-studded event, and spoke with some of the alums about their most memorable moments from their Idol journeys.

Justin Guarini -- who finished as the runner-up behind Kelly Clarkson during the show's first season -- spoke with ET's Matt Cohen about returning to the Idol stage, and how it felt.

"Being back on the stage -- that looks nothing like the stage that I was on by the way, they put a little budget into it this year and the years since I've been on it -- it's amazing to be back and see that the energy hasn't changed," Guarini shared.

"My favorite memory from my time on Idol has to be my very first performance that I did live on television, because we didn't really know if [the show] was going to be anything," he recalled. "But it felt so beautiful, so wonderful, and it was just the beginning of 20 years of an amazing [journey]."

Looking back at his most cringeworthy moment, Guarini explained how his biggest misstep also proved to be one of his greatest learning experiences.

"The one moment that I just learned so much from was when I messed up the lyrics of 'Route 66.' It was our first big band night, the first time we had a live band," he recalled. "I messed up the lyrics but I just kept going and I ended up working my way out of it."

"Because there was no social media like we know it, there was no, sort of, people watching my every move. I made it through and it just taught me to trust myself and taught me to trust the process," he added. "And it's one of my favorite moments."

As for Lauren Alaina -- who came in as the 10th season's runner-up -- her favorite memory was "probably when I fell down the stairs!"

"I fell down the stairs, I was running and it was not a good idea, and I mean all the way down the stairs, broke the pinky, all the things," Alaina recalled. "To this day, people ask me about the falling down the stairs. So it actually showed America that I'm a big goofball and I still get to laugh about it now."

Reflecting on the special episode, Ruben Studdard -- who won the second season of the series -- said with a smile, "It was really amazing, like, just to be in the room. It felt like just a big high school reunion, to be here."

One recurring theme, when it came to looking back on the early days of the show, seemed to be questionable style choices. Many of the alums are still embarrassed by the fashion of the day -- and even host Ryan Seacrest, who has been with the show since the start, some style decisions are baffling.

"It seemed like a wise choice at the time," Seacrest said when asked about opting for frosted tips in the early seasons. "When one looks back, one realizes one has made many mistakes in their career, and that was a big one. I would never rock that hair again."

American Idol season 20 airs Sundays and Mondays at 8 p.m. ET/PT on ABC.