UFC's Michael Chiesa Explains Ditching Mullet, 'I Have a Girlfriend Now'

All good things must come to an end ... and Michael Chiesa's signature mullet is no exception ... and the UFC fighter is telling TMZ Sports he chopped off his hair at his girlfriend's request!!!

Chiesa has been rockin' the "business in the front, party in the back" look for years ... but the welterweight cleaned up his look and got rid of the mullet recently ... and now we know why.

"It's just time for me to grow up. I've had a mullet the better half of my whole life. I've always just been this hairy, wild man," Chiesa says.

"I have a girlfriend now, and as she's gotten more comfortable in the relationship, she wants a civilized looking boyfriend ... it's good for me, man."

Maverick -- who is fighting Diego Sanchez at UFC 239 next weekend -- says although he doesn't care what people think about him, it's about time he looked the part of being a professional.