The good doc's showed off his apparently clean-shaven mug on Twitter, posting before-and-after pics that are sure to drive his fans wild. While the new look seems totally legit at first glance ... we gotta take April 1 into account.

Tom Brady already used the social media platform to stage a fake retirement announcement.

Of course, if Phil is just yanking our chains with another April Fools' joke, he's really going ALL in with shaving cream, razors, a bib and some makeup magic ... but hey, maybe he's just doing a little spring cleaning.

Worth noting -- he didn't post any video of the slaying of his mustache, which makes us suspect.

If you're already missing Dr. Phil's old look, chill ... it'll grow back ... if it's even really gone.

In the meantime, enjoy the baby face.