Jonathan Groff, Glee Jonathan Groff, Glee

Before Glee, Jonathan Groff would have not been able to sing Adele's guttural, smoldering anthem of heartbreak, "Rolling in the Deep," which he used to swagger back onto the hit show last week. The actor, previously best known for his work in New York theatre, says it was Glee that taught him to rock out.

"The first song I sang with Vocal Adrenaline was 'Highway to Hell' and I remember calling [music producer] Adam Anders and saying, 'Maybe we should sit down with a piano instead because I don't sing like this,'" Groff tells "But he pulled out this side of my voice I didn't know existed, this rock scream. It has totally changed the way I sing."

It was that rock edge that accompanied the return of Groff's Jesse St. James. A year ago, the devious show choir wonderboy made Rachel swoon to Lionel Richie's tender come-on "Hello," but since then he broke her heart, and deprived New Directions of a victory — so only Adele's pissed-off, breakup-mourning duet would do. Still, the 26-year-old actor says going back to Glee was as much of a surprise to him as it might have been to viewers who remember the cruel way his character ended things with Rachel: Right before leading Vocal Adrenaline through a title-clinching rendition of "Bohemian Rhapsody," Jesse revealed his true colors, smashing an egg on Rachel's head and dumping her.

"Totally harsh," Groff says. "I remember reading the script and being like, 'Oh my God, that just happened. Okaaaay.'"

Jonathan Groff returns for Glee finale... and Rachel

But having convinced Rachel in Tuesday's episode that he was a changed man — now a college drop-out with glee club still on the brain — he's returned to McKinley High to help coach New Directions before Nationals, and possibly woo back Rachel. (Don't bother asking if his plan works, Groff's not telling. Also, he adds, "I just finished my first day of shooting. I've sung one song with Lea, so I also honestly don't know," he says.)

In any case, the offer to reprise Jesse couldn't have happened at a better time. Groff has kept busy since his last appearance, making his West End debut in a production of Ira Levin's Deathtrap, but he'd been contemplating a move from New York to Los Angeles to pursue more film and television roles. His resume, while short, boasts being cast by Ang Lee as charismatic concert promoter Michael Lang in 2009's Taking Woodstock and Robert Redford in this year's Civil War-era thriller The Conspirator.

Fortunately while he worked in the UK, he kept up with Glee's second season via iTunes. "Because I love it, not because I thought I'd necessarily be back," he says.

"Glee had been the longest job I'd ever done in front of the camera, and I really enjoyed it," Groff continues. "It felt like it was time to take a risk and move out here to L.A., try and get some film and television going.  I'm still keeping my place in New York because I couldn't bear to give it up, and I love doing theater."

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In the meantime, he's already been won over by the West Coast. "I think as a New Yorker — and I have been one for the past six years — you're trained to have an attitude about L.A., but I have to say, I'm loving it. When I did Glee last year, I was here for four months and I took swimming lessons at UCLA, I trained to do a triathlon, I hiked in Malibu. I started to be like, 'Wow, California has some great things to offer.'"

There was also the allure of working again with real-life best friend and former Spring Awakening co-star Lea Michele, as well as Glee executive producer Ryan Murphy, who first cast Groff in his 2008 FX drama project Pretty/Handsome, about a married father of two desperate for a sex change operation. (It was then that Groff introduced Murphy to Michele.) Glee, he says, is Murphy incarnate.

"Ryan, to me, is sort of like this really fascinating contradiction," he says. "When I watched Glee for the first time, I thought, 'Wow, this is him in a nutshell.' It's really smart and snappy and slick and witty and funny, and, like, really biting, but then it also has this unexpected heart."

And while critics have been up and down on some of the Season 2 story lines, Groff says Glee's mainstream appeal can only be considered a good thing. "For being one of the most popular television series on today, and with all the young people watching it, it's amazing how they're pushing the envelope the way they are. I feel like we're so lucky to have a show like it on TV," he says, pointing to the show's sensitive handling of issues like sexuality and bullying. "Critics are going to say what they're going to say, but I feel like the show is so creative and fun and moving — and on top of all that, it's also brave."

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And Groff knows something about going up against critics: A year ago, he made national headlines when a columnist for Newsweek wrote that the openly gay actor was perhaps too gay to convincingly play Rachel's straight, show choir-loving boyfriend. The essay, "Straight Jacket," really ticked off Murphy, but Groff — ironically Tony-nominated just three years prior for playing a very hormonal, very straight teen in Broadway's Spring Awakening — says he just shrugged it off.

"I feel the same way about the Newsweek article now as I did then — you just can't let it affect you. I treated it as a bad review, which I've gotten plenty of in the past," he says, adding he put the Newsweek story behind him almost as soon as it came out. "It's one of those things that ends up in print, and you shrug and keep doing the work. Fortunately, I've been able to continue doing that."

For now, that means figuring out the enigma that is Jesse. Groff says Murphy threw him a curve ball in creating the rival singer, a self-assured schemer and mega thespian whose love of musical theater won over Rachel but fooled none of her fellow glee clubbers.  "He was described as a manipulative, maybe evil guy whose team sang crazy rock songs," Groff says.  "I remember Ryan saying to me, 'I want to write a part that's nothing like you in real life. I want it to be challenging for you, and I want you to sing songs that are hard for you.' It doesn't sound nice, but it really was."

And despite Jesse's previous treatment of Rachel, viewers don't seem to be holding it against the actor. When he decided to watch last summer's Glee concert tour in L.A. from the audience, he was immediately recognized — and then surrounded by Jesse fans. Security was unprepared. "That was so funny. It never once occurred to me that something like that would happen," Groff says. He later rewarded them with a surprise performance.