Another Lost alumnus is heading back to Hawaii.

William Mapother, who portrayed creepy island resident Ethan Rom on the ABC hit, will appear on an episode of Hawaii Five-0 Season 5 this fall.

According to CBS sources, Mapother will portray Eric Porter, a well-liked, rich business owner who becomes entangled in a painfully tense situation… yet offers his help to the authorities.

Mapother - who has also guest-starred on The Mentalist, Mad Men and Caste - is the NINTH former Lost cast member to appear on Hawaii Five-0.

He joins Daniel Dae Kim, Terry O’Quinn, Jorge Garcia, Henry Ian Cusick, Sam Anderson, Tania Raymonde and François Chau.

Hawaii Five-0 returns with new episodes on Friday, September 26.

Matt Richenthal is the Editor in Chief of TV Fanatic. Follow him on Twitter and on Google+.