Complex sentence: He ended up taking a year off from college to play the role of Cormac McLaggen in the Harry Potter film series: he was cast in his break-out role as Cormac McLaggen in the film Harry Potter and the Half-Blood Prince.
Split into simpler sentences: He ended up taking a year off from college to play the role of Cormac McLaggen in the Harry Potter film series. He was cast in his break-out role as Cormac McLaggen in the film Harry Potter and the Half-Blood Prince.