Allen was able to claim Idol's eighth-season title based on the "just under 100 million" home viewer votes that were cast immediately following Tuesday night's live performance broadcast that saw Allen and Lambert each sing three songs.
"Are you serious?! Are you friggin' serious?!" exclaimed Allen after the results were revealed.
"The underdog -- the dark horse -- comes back and wins the nation over," said host Ryan Seacrest. "How does it feel?"
"It feels good man. But Adam deserves this," responded a subdued Allen. "I'm sorry. I don't even know what to feel right now. This is crazy. Thank you so much."
Last week, Cowell commented that Allen was "not a good enough singer to compete with Adam" in the finale and added "the only one who can compete with Adam on vocals is Danny."
However home viewers disagreed, as Gokey was ousted from the competition during last Wednesday night's live results show. In addition, Seacrest had stated "just over one million votes" had separated Allen and Lambert in the vote to determine the Top 2.
During Tuesday night's final eighth-season performance episode, both Lambert and Allen performed three times -- singing their favorite previous song from the season; a song selected for them by Fuller; and "No Boundaries," a new song co-written by Idol judge Kara DioGuardi that will serve as the winner's debut single.
Cowell "scored" the first round of performances for Allen, who sang "Ain't No Sunshine," which he first sang as a member of the Top 9.
"Well, Kris, look, I think we just have to remember right now that this is a competition, right?" commented Cowell. "I'm going to be honest with you, when your name was announced last week I wasn't sure whether America had made the right choice. I'm being honest. But I absolutely take all that back now after that performance."
However Cowell would subsequently score the second round of performances for Lambert, who wowed the judges with his rendition of "A Change Is Gonna Come," which was chosen for him by Fuller.
"Adam, all I would say after that is you are 100% back in the game, congratulations," commented Cowell.
Both finalists' renditions of "No Boundaries" received mixed reviews, however Cowell used Lambert's final performance to made it clear he thought Lambert still deserved to win the competition.
"Over the entire season you have been one of the best, most original contestants we've ever had on the show," Cowell told Lambert. "And the whole idea of doing a show like this is that you hope that you can find a worldwide star. I genuinely believe with all my heart that we have found that with you, congratulations."
While Cowell said he was proud of Allen's growth, he gave him more of a conciliatory congratulations.
"I think watching you tonight on this stage has been incredible because I could remember your first audition where you came in no confidence [and] weren't sure how good you were," Cowell told Allen. "Your mom and dad's face tells me everything -- they're very, very proud of you, as they should be -- and you have thoroughly, thoroughly deserved to be standing on this stage tonight, congratulations."
However similar to last week, home viewers once again disagreed with Cowell and crowned Allen the champ.
"I would just say to both of you -- and I don't normally mean this -- [that] I thought you were both brillant, [are] unusually nice people, and I think that both of you should be very proud of what you acheived last night and the future is all yours," Cowell said before Seacrest revealed Allen's victory.
All of Idol's Top 13 eighth-season finalists participated in the finale, singing Pink's "I'm a Rock Star" as a group before performing "Smooth" with Carlos Santana. The Top 7 male finalists also performed Rod Stewart's "Do Ya Think I'm Sexy?" while the Top 5 female finalists performed a medley with Black Eyed Peas.
The 127-minute filler-filled broadcast also included the eighth season's final Ford music video; video montages of Allen and Lambert's Idol journeys; live updates with Allen aficionados in Conway, AR and Lambert fans in San Diego, CA; Allen and Lambert performing a duet with Queen; Gokey performing with Lionel Richie; fourth-place finisher Allison Iraheta performing with Cyndi Lauper; fifth-place finisher Matt Giraud performing with Santana; sixth-place finisher Anoop Desai and eleventh-place finisher Alexis Grace performing with Jason Mraz; a duet by seventh-place finisher Lil Rounds and Queen Latifah; and ninth-place finisher Megan Joy and tenth-place finisher Michael Sarver performing with Steve Martin.
Viewers also saw Allen and Lambert each receive a new Ford Fusion Hybrid; Allen perform with Keith Urban; DioGuardi perform with "Bikini Girl" Katrina Darrell; Lambert perform with KISS; Cook sing "Permanent;" Stewart sing "Maggie May;" and the return of the Golden Idol Awards, which (mercifully) were not included in last year's finale.
The finale broadcast concluded with Allen singing "No Boundaries."
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