Complex sentence: It is found out later in the series that it is owned by the other Future Trunks and he was killed by Cell after that Trunks killed Android 17 & 18 in his own timeline.
Split into simpler sentences: It is found out later in the series that it is owned by the other Future Trunks and that he was killed by Cell. After that, Trunks killed Android 17 & 18 in his own timeline.