Complex sentence: On the accession of Ptolemy Philadelphus, Demetrius fell into disfavour (he apparently supported the wrong candidate, Ptolemy Keraunos), and was sent into exile to Upper Egypt, where he is said to have died of the bite of a snake.
Split into simpler sentences: On the accession of Ptolemy Philadelphus, Demetrius fell into disfavour (he apparently supported the wrong candidate, Ptolemy Keraunos), and was sent into exile to Upper Egypt. He is said to have died of the bite of a snake.