Board Thread:Wiki Discussion/@comment-28440466-20160512075843/@comment-5956954-20160512091441

It's never stated how long it took for Mettaton to achieve stardom, and Alphys complains that Mettaton mostly abandons her after that has happened. It's entirely plausible that the friend could be Mettaton.

Combine that with the process of narrowing down who the friend could be: they need to be male, live a sort of hedonistic/ostentatious lifestyle, and would be willing to lay around "seductively." Mettaton is the only character that fits that description. Well duh. Told ya I was probably wrong.