Board Thread:Wiki Discussion/@comment-28440466-20160512075843/@comment-27701762-20160512090530

Cheeseskates wrote:

PancryPancreas5 wrote: She's not talking about Alphys there, she's talking about her friend who's most likely Mettaton... Can't really be Mettaton. Once Mettaton got the body, he decided to leave Alphys for stardom. Regretted it, though. I am probably wrong, though, because there is no time in undertale where it is implied Mettaton went to stardom and when he got the body to "lie on the piano seductively." 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.