The episode airing Oct. 11 also will explain what happened to Locke, Desmond and Eko, played by Terry O'Quinn, Henry Ian Cusick and Adewale Akinnuoye-Agbaje respectively, when a hatch collapsed on them in last season's finale. Hurley, played by Jorge Garcia, also returns to camp after being released by the "Others," Zap2it.com reported Thursday.
Somerhalder's character, Boone, has been dead since the first season of "Lost," but Somerhalder has appeared on the show in flashback scenes involving his onscreen sister, Shannon, played by Maggie Grace.
Shannon was killed off in November 2005 and Boone's return to the show means he probably fits into one of the other islanders' pasts as well, said Zap2it.
Somerhalder also stars in the miniseries "Marco Polo" as the famous explorer.
Notable deaths of 2014 [PHOTOS]
'Glee' star Matthew Morrison weds in Hawaii