We've seen him in briefs and in boxers, even in the combination of both - boxer briefs.
The swimmer has been pictured sporting well known brands - Calvin Klein, Hugo Boss, Speedo, and Under Armour - that just perfectly fit the most decorated Olympian in history.
Phelps has been in mainstream underwear ads that were featured ahead of the Olympic Games.
But did you know that he was also busted for reportedly wearing women's underwear?
Of interest, in celebration of Michael Phelps' 28 Olympic medals, FOXSports.com shares 28 facts about his already unbreakable record.
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