During Matthew Morrison's June 13 concert in London, the 'Glee' star was joined by former 'N Sync member JC Chasez for a cover of the boy band's 2000 ballad 'This I Promise You.'

The 32-year-old actor, who just released his debut solo album in May, kicked off the rendition by singing Justin Timberlake's opening verse amidst a smoke-filled backdrop. The sold-out crowd at the Hammersmith Apollo seemed quietly mesmerized until Morrison introduced his pal to the stage.

"Ladies and gentlemen, my friend, JC Chasez," he said as the audience went wild. The 34-year-old performed his original verse with ease, and finished out the song with the help of Morrison, who tackled harmonies and split the bridge with the 'America's Best Dance Crew' judge.

Morrison co-wrote songs for his self-titled full-length with the 'N Sync singer two of which ended up on the final tracklist. Chasez boasts writing credit on 'Hey' and 'Don't Stop Dancing.'

"I've definitely teamed up with some great producers, some great songwriters," Morrison told MTV while he was working on his album last September. "And yeah, I just did this great song last week with JC Chasez that was very, very cool. It turned out really well. He's such a good songwriter."

Watch Matthew Morrison Perform 'This I Promise You' With JC Chasez