Complex sentence: In 2015 an unfinished version of "Boston" was illegally leaked online, however, it has still never been aired and has never been formally released to the public in any format by legally by Adult Swim.
Split into simpler sentences: In 2015 an unfinished version of "Boston" was illegally leaked online. The episode has still never been aired and has never been formally released to the public in any format by legally by Adult Swim.