before 1000;Middle English,Old Englishelles (cognate with Old High Germanelles), equivalent to ell- other (cognate with Gothicaljis,Latinalius,Old IrishaileGreekállos, Armenian ayl other; cf. eldritch) + -es -s1
The possessive forms of somebody else,everybody else, etc., are somebody else's, everybody else's, the forms somebody's else, everybody's else being considered nonstandard in present-day English. One exception is the possessive for who else, which is occasionally formed as whose else when a noun does not immediately follow: Is this book yours? Whose else could it be? No, it's somebody else's.
O.E. elles "other, otherwise, different," from P.Gmc. *aljaz (cf. Goth. aljis "other," O.H.G. eli-lenti, O.E. el-lende, both meaning "in a foreign land;" see also Alsace), an adverbial genitive of the neut. of PIE base *al- "beyond" (cf. Gk. allos "other," L. alius; see alias). Synonym of other, the nuances of usage are often arbitrary.