'American Idol' Series Finale Recap: Alumni Cameos and Star-Studded Performances

The series finale include many blasts from the past, and its final winner.

Host Ryan Seacrest revealed that Trent Harmon is the winner of the Fox show’s 15th and final season. La’Porsha Renae came in second.

Here are Thursday’s highlights:

Seacrest took the stage and introduced Brian Dunkleman, who served as his co-host for the show’s first season but didn’t stick around for subsequent seasons. Dunkleman joked that he knew the “pain of life without Idol,” but assured Seacrest that being unemployed “is not that bad.” When Seacrest noted that he had “a radio gig and some other stuff going on,” Dunkleman replied, “That’s what I said too.”

La’Porsha and Trent then teamed up for “It Takes Two,” first performed by season-one finalists Kelly Clarkson and Justin Guarini.

The pregnant Clarkson couldn’t attend in person, but appeared in a pre-taped segment performing a medley of her hits that included “Miss Independent,” “Breakaway,” “Since U Been Gone,” “Because of You,” “My Life Would Suck Without You,” “Don’t You Wanna Stay,” “Stronger (What Doesn’t Kill You),” “Heartbeat Song” and her winning single, “A Moment Like This.”

Several of the show's rockers, including Chris Daughtry, Bo Bice, Maroulis and season-13 champ Caleb Johnson, joined forces for a rock & roll medley.

Judge Keith Urban got into the act, teaming up with Carrie Underwood for the Stevie Nicks and Tom Petty duet, “Stop Draggin’ My Heart Around.”

Next, "Idol" country artists, among them Diana DeGarmo, Bucky Covington, Lauren Alaina, Kellie Pickler and Scotty McCreery, took center stage for a medley of country hits.

Judge Harry Connick, Jr. brought Ellis Marsalis Center for Music student and fellow New Orleans native Marley Fletcher onstage to perform a duet of Louis Armstrong's "What a Wonderful World." Fletcher is one of the beneficiaries of "American Idol" charities, which have raised over $185 million for children in underserved communities.

Judge Jennifer Lopez followed with a medley of songs from her All I Have residency at Caesars Palace in Las Vegas, including “Ain’t Your Mama” and “Let’s Get Loud.”

LaToya London, Fantasia Barrino and Jennifer Hudson -- season three's "Three Divas" -- reunited for an a cappella performance of Simon & Garfunkel's “Bridge Over Troubled Water.” Hudson followed with “Remember the Music,” her song from the Fox drama Empire. Brandon Rogers, Clark Beckham, Danny Gokey, George Huff and Elliott Yamin continued the nostalgic trip with The Temptations' "Ain't Too Proud to Beg." Fantasia delivered a solo performance of her single “Ugly,” and then London came back out to sing Aretha Franklin and George Michael's "I Knew You Were Waiting (for Me)" with Taylor Hicks. Joshua Ledet from season 11 then sang James Brown's “It’s A Man’s Man’s Man’s World.” Season-12 winner Candice Glover and season six’s Melinda Doolittle closed out the medley.

Seacrest then got a surprise visit from William Hung, who bounded onto the stage to sing his audition song, “She Bangs,” by Ricky Martin.

Underwood closed out the performances with her 2014 hit, “Something in the Water.”