Chris Colfer Joins Darren Criss for 'Baby It's Cold Outside' at Royal Albert Hall

Chris Colfer joined Darren Criss onstage at London's Royal Albert Hall for a surprise duet of "Baby It's Cold Outside" during Criss's one-night-only concert, reviving the pair's "Glee" characters, Kurt Hummel and Blaine Anderson.

Criss began the song alone. He told the audience he would sing both parts, even though "it's not supposed to be like that, but I've managed to pull off so many things," he said. Colfer walked out a few verses later. "The only thing inappropriate about doing this song is doing it without me," Colfer joked before singing.

Where does the song come from?

The two actors first performed the duet in Season 2, Episode 10 of "Glee," titled "A Very Glee Christmas," which aired in 2010. Kurt and Blaine became fan favorites on the series. Their characters began dating in Season 2, got engaged, and married in the show's final season.

Is a 'Glee' reboot actually happening?

The reunion lands weeks after "Glee" creator Ryan Murphy confirmed that a reboot script exists. "Well, funny you ask, 'cause I just finished the script an hour ago," Murphy told Entertainment Tonight last month. "So, we have a script. Brad [Falchuk], Ian [Brennan] and I, who wrote all the first two seasons, have written something. I've been in touch with around 10 of the original cast members. It's very sweet, and they all had a lot of questions, but they all were very enthusiastic about the idea."

Murphy added a caveat: "nobody's read it." He continued: "So I don't know, we'll see. I vowed to myself that I wanted to write a couple of them to see what people think, particularly the cast, 'cause we were very close when we were making it."

What does this change for fans?

What does this change for viewers of the original series? A finished script, roughly ten cast members in contact, and no readers yet — a project in motion, but far from greenlit. The Royal Albert Hall duet, staged without announcement, shows the two actors can still deliver the material that made their characters central to the show.

"Glee" premiered in September 2009. The cast included Lea Michele, Colfer, Criss, Cory Monteith, Naya Rivera, Dianna Agron, Matthew Morrison, Jane Lynch and Heather Morris, among others.

Whether Murphy's script reaches the screen may depend on the cast's response. As he put it, the original team "were very close when we were making it" — and that closeness now sits at the center of any revival.