The singer, 37, who rose to fame with the pop-punk band which produced hits including “Year 3000” and “Crashed The Wedding”, performed in disguise as Rhino throughout the ITV series.
Simpson performed three times across Saturday’s finale show (18 February) and beat Kaiser Chiefs frontman Ricky Wilson, who was disguised as Phoenix, and All Saints star Natalie Appleton, who was hiding behind the Fawn mask.
The Busted star admitted he did not expect to win the show and just tried to “remember the lyrics and have fun”.
Asked how he found the experience, he said: “I was terrified the entire time because the thing I was scared most of was remembering lyrics. I often forget lyrics to my own songs.”
He added that his last song of the show, “Try” by P!nk, was the only time he did not really think about the lyrics and he just tried to enjoy himself.
Simpson had the judges fooled along the way but Rita Ora and Davina McCall correctly guessed his identity at the end.
Jonathan Ross thought it could have been singer James Arthur while guest judge Lee Mack opted for George Ezra.
Simpson was the first to perform solo on the night, delivering a powerful rendition of “Before You Go” by Lewis Capaldi while dressed as a cowboy.
Ora said Rhino had her “favourite voice in the whole wide world” before guessing it could be Simpson behind the mask.
Former contestant Harlequin, who was previously revealed as singer-songwriter Gabrielle, also returned to sing “Beneath Your Beautiful” by Labrinth alongside Rhino and she guessed it could also be Arthur.
Alongside his time in Busted, Simpson was also a member of the rock band Fightstar and released music as a solo artist.
After his reveal, the singer admitted that his bandmates in Busted and Fightstar all guessed it was him behind the mask “within the first two seconds of hearing Rhino sing”.
“When you spend that much time on stage with people and spend so much time in the studio, it would be very hard for them not to get it pretty much instantly”, he added.
Simpson, who has two children with his wife Anna Barnard, revealed he decided to do the show for his family, saying: “I thought it would be something that my kids would love to watch and also it looked like a really fun show to do.”
After Kaiser Chiefs singer Wilson placed second, he confirmed he had enjoyed his time on the show, saying: “It gets quite infectious. You really want to win it.”
Ora was in shock that he was behind the mask as she has worked alongside Wilson in the past, adding: “If you sang how you sing I would have got you in a second.”
The singer also said he was “very pleased” to be mistaken for actor David Tennant by McCall.
For his first performance, he sang “Sway” by Michael Buble accompanied by dancers in white suits and bird masks while he donned bright red and orange feathers.
Mo Gilligan thought he was a “great showman” which made him consider DJ Mark Ronson, with Take That’s Mark Owen and Razorlight’s Johnny Borrell also among the guesses.
Presenter Denise van Outen also returned as Fox to perform Elton John and Kiki Dee’s “Don’t Go Breaking My Heart” with Phoenix, and she thought the red feathers were a clue to it being comedian Leigh Francis, aka Keith Lemon.
All Saints singer Appleton was the first celebrity to be unmasked during the final and McCall admitted she had all the judges “flummoxed” about her true identity.
While Ross said: “We don’t get to hear your voice like that that often, where you’re singing those ballads. What an amazing act.”
Following her reveal, Appleton said: “I loved fooling you guys, it was such a buzz” and that she had enjoyed Gilligan mistaking her for country star Shania Twain.
She added: “I had the best time, it’s been amazing. I do recommend.”
Fawn performed twice throughout the finale, firstly with an elegant performance of “Hopelessly Devoted to You” from 1978’s Grease, dressed in a polka-dotted outfit with a matching bow.
The power of her voice led Ross to believe it could be All Saints singer Shaznay Lewis while McCall thought it could be singer Samantha Fox.
Mack opted for actress Jenna Coleman and Ora guessed actress Suzanne Shaw was behind the mask.
Welsh singer Aled Jones also reprised his Traffic Cone costume to duet with Fawn on “When She Loved Me” by Sarah McLachlan, who thought former Spice Girl Emma Bunton could be the secret star.
The three finalists opened the show with a lively performance to “We Can Be Heroes” to kick off the night.