Jonathan Knight tweeted "I'm sorry......" after leaving the stage Thursday night during New Kids on the Block's concert in New York.
According to Billboard, when the band's iHeartRadio's set began, Jonathan was visibly out of sync with the band, and repeatedly kept moving to the back of the stage. He even seemed to receive a cell phone call during the set!
His fellow singers put their arms around him and joked to put him at ease. At one point, Jordan Knight tried to get his brother to join in and sing "Survive You," and Jonathan started to sing and laughed a bit, then stopped. He left the stage while the band continued to sing. They said Jonathan would return, but he didn't.
Jonathan has been open with his struggles with anxiety and panic attacks, so it's possible his social anxiety took over. Watch the concert, and hear the fans’s cheers of support for Jon, in a video here.
Sources: Billboard, @JonathanRKnight