Usher Joined Onstage by Trey Songz at Chicago Concert

Trey Songz made a special appearance when Usher brought his "UR Experience" tour to Chicago on Monday night, November 17. Taking the stage at the city's United Center, the two R&B superstars excited the crowd with a remix to "I Luv These".

August Alsina, who served as an opening act on the tour, returned to the stage and joined the duo for the performance. Trigga, who surprised concertgoers mid-song, then told the crowd that he went on a tour with Usher a few years ago and it changed his life.

"Make some noise for one of the greatest in the game - greatest there ever is, greatest there ever will be. I love you, boy," he said.

Trey wasn't the only surprise guest during Usher's United Center gig. The coach of "The Voice" also brought out Rico Love to perform his single "They Don't Know".

While hitting the road for his "UR Experience" tour, Usher continues working on his highly-anticipated new album "UR". The LP, which was initially planned for release later this year, has been delayed indefinitely