The Brooklyn teen on trial in the fatal shooting last year of an innocent man on a city bus took the stand Tuesday, causing his victim’s widow to flee the courtroom in tears before returning.

Kahton Anderson, 15, allegedly fired a .357 magnum at rivals, with a stray bullet killing hardworking family man Angel Rojas, 41.

His testimony gave prosecutors a chance to introduce a chilling selfie of Anderson grinning as he points the gun that would later kill Rojas while sporting the same hat he wore during the shooting.

Rojas’ widow Maria Lopez, 43, began sobbing when Anderson took the stand, and left the court before returning.