Mystery Revealed

Goku is asked by the mysterious stranger to speak in private and then has his Super Saiyan strength tested. Once the stranger is satisfied, he reveals his name is Trunks, he is Bulma and Vegeta's son, he came from a grim future, explaining Goku will die from a heart disease and all the Z Fighters, except Gohan, will be killed in three years by androids created by Dr. Gero. After giving Goku the disease antidote, Trunks returns to his own time, leaving Goku to explain to the Z Fighters what lies ahead.