WARNING: THIS VIDEO WILL MAKE YOU CRY!!!
NY Mets superstar Pete Alonso surprised a sick fan with a video message -- and the gesture was so heartfelt, it brought her to tears!
The story behind the footage is touching ... shortly after 82-year-old Kathleen Selig tragically learned she was given just weeks to live after a small cell lung cancer diagnosis, her granddaughter reached out to the Mets over social media.
18-year-old Ally Henglein explained of her "Gammy," "She is a diehard Mets fan and has been since the start.