Where'd All of Matt Damon's Hair Come From?

Matt Damon's either got a serious addiction to Rogaine or sporting extensions because a man bun and full head of hair have appeared out of thin air.

The "Jason Bourne" star made a promo appearance Tuesday in Beijing looking wayyy hairier than he did less than a month ago. The quick change could no doubt be a plug for a hair growth product, but there's a more likely explanation.

We're guessing re-shoots for "The Great Wall," which was shot entirely in China.

Sorry, Minoxidil ... find another mark.