DBZ Episode 122
From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
Mystery Revealed is the fifth episode of the Trunks Saga and the one hundred twenty-second overall episode in the uncut version Dragon Ball Z series. The original Japanese title is "Boku no Chichi wa Bejiita desu... Nazo no Syonen no Kokuhaku" (ボクの父はベジータです... 謎の少年の告白). The episode first aired on January 15, 1992. It's original American air date was September 8, 2000.
Goku is saying hi to his friends when Vegeta says that this mysterious kid can turn into a Super Saiyan even though Vegeta, Goku, and Gohan are the only remaining Saiyans. He also asks if Goku knows him because the kid knew when he was coming and knew much about him. Goku doesn’t know him and the mysterious man asks Goku for a word alone.
They walk off and the man who says he is Trunks asks Goku to become a Super Saiyan. Goku is surprised, but does it and so does Trunks. He then starts swinging his sword at Goku, but Goku blocks all of them with his finger. The boy says that now he can trust him with his life and that everything they say about him is true. Meanwhile the other guys (Vegeta, Piccolo, Krillin, etc..) are getting worried. Future Trunks says that he wouldn’t have had to come if Goku had come 2 hours earlier. Goku says that he could have hyper warped if he knew he had to. It is a technique he says he learned from a planet on his way home. Future Trunks says that he comes from the future. He says that his dad is Vegeta and his mom is Bulma. After hearing this Goku falls down with laughter, but eventually pulls himself together. He says that in the future the Earth is being destroyed by these horrible Androids created by Dr. Gero, a member of the Red Ribbon Army. They ended up turning on their master and kill him. Future Trunks says that the Androids have extremely amazing powers. He admits that he himself, a Super Saiyan is running from them because they are so powerful. He tells Goku that in 2 years he will be born. Earth will start a war against them and Tien, Yamcha, Piccolo, Krillin, Vegeta, Chiaotzu, and Trunks' master, Gohan will be killed. Goku asks about himself and Future Trunks says that he will be killed by a horrible virus. Goku gets mad that all his powers will be wasted all because of a virus and he won’t be able to fight the war. Then Future Trunks says that in the future there is an antidote and he tosses a capsule to Goku. He says that when he gets the virus eat the capsule and he’ll be fine. Then he says not to tell anybody these secrets he told him since Bulma and Vegeta might not have Trunks if they find out. Then he warps away to the future. When Goku comes back he says it was nothing, but Piccolo says that he heard the whole conversation with his excellent hearing. He tells Goku that he is going to tell everybody so that they can prepare for the war and maybe not die. Piccolo tells them everything except about Bulma and Vegeta having Trunks. They all agree that they will train their hardest for the war.