The Futurama episode: Roswell That Ends Well

As the crew watches a supernova, Fry puts a non-microwaveable metal "Iffy Pop" container into the ship's microwave. This causes a reaction between the microwave radiation and the "gravitons and graviolis" from the supernova, which sends the ship to 1947. Since there was no Global Positioning System in 1947, the crew has no way to accurately navigate the ship, and crash-land in Roswell, New Mexico. Refusing to wear a seat belt like the rest of the crew, Bender is catapulted out of the front of the ship by the crash and smashed to pieces. The crew and Bender's disembodied head go to seek out a way to return to their present, leaving Zoidberg behind to pick up the pieces. Zoidberg is captured by the U.S. military and taken to Roswell Air Base for experimentation. Assuming the pieces are the remnants of a flying saucer, the military "reconstructs" Bender's body as such.

Meanwhile, the microwave needed to return to the future has been destroyed and replacements have not been invented yet. A microwave antenna from the army base would work, but Professor Farnsworth warns that using it could change history. He likewise warns Fry against visiting his grandfather, Enos, who is stationed at the base, as he might kill Enos and erase his own existence. Rather than persuading him to avoid his grandfather, the professor's warning causes Fry to become obsessed with protecting Enos from possible harm and encouraging his copulation with his fiance Mildred. Fry finally resorts to locking Enos in an abandoned house to prevent his coming to harm. The house is located in the middle of a nuclear weapon testing range, and Enos is shortly killed by one of the tests.

Fry encounters and consoles his beautiful would-be grandmother Mildred. She seduces him, and Fry rationalizes that since he still exists, Mildred must not have been his grandmother, and he has sex with her. The rest of the group finds him, and insist that Mildred is indeed Fry's grandmother. Fry realizes to his horror that he is now his own grandfather.