Katherine Jenkins was mugged in southwest London after trying to help an elderly woman being attacked by a violent girl gang, her agent said.
The 39-year-old opera singer was on her way to a rehearsal at 3.10pm on Wednesday when she witnessed an elderly woman being attacked on King's Road, Chelsea.
After she stepped in to help - in what was described as an "extremely violent" incident - the singer was mugged herself.
The Welsh mezzo-soprano was in London to sing at the Henry van Straubenzee charity carol concert at St Luke's Church in Chelsea.
Her agent said: "Miraculously, Katherine still managed to perform at the concert as she didn't want to let the charity down."
According to the Mail Online, the singer was visibly close to tears as she waited for officers to arrive at the scene.
She was later able to help police identify the attackers, the Mail added.
The Met Police said it was called to reports of a robbery on King's Road in Chelsea at about 3.10pm on December 4.
Officers attended the incident and arrested two 15-year-old girls on suspicion of robbery, a police spokeswoman said.
Adding: "A female member of the public had attempted to intervene."
An officer was assaulted during the incident but did not require hospital treatment.
The older girl was seen trying to escape, shouting at the top of her voice and causing a scene.
The two girls were released under investigation, but one was re-arrested on December 5 in connection with the same incident after further information was received. She remains in custody.
In a statement, Jenkins' agent said: "Katherine was in London to sing at the Henry van Straubenzee memorial charity carol concert at St Luke's Church.
"On her way to rehearsal she witnessed an older lady being viciously mugged and intervened to help.
"As a result of her stepping in, Katherine was then mugged herself.
"However she helped the police identify the perpetrator and the young woman was arrested shortly afterwards."
Additional reporting by Press Association