No.1 fan

Does anyone know who The Lettermen are? They're waaaaaayyyyyyyyyy before my time. My parents are huge fans so they watched the concert last night. Guess who ended up on stage. I don't know how my Mom (the one in yellow) and my Tita managed to be up close and personal with the performers but they did. I also don't know how my Mom got up on stage considering she has a fractured foot. But then again, if I was in a concert of someone I super love the music of, I would have done a free run to the stage.