A Dodger fan now has a tattoo of a player on his favorite team's rival ... and it's all 'cause the outfielder got surprisingly traded from L.A. just days after the ink went on the skin.

Here's the deal -- a fan was at the Dodgers' spring training workouts in Arizona earlier this month, when he asked both Cody Bellinger and Matt Beaty to sign their names on his arm.

In exchange for the autographs, the fan promised to get the sigs tattooed permanently -- so the players obliged.

A short time later, the fan went under the needle -- and the tattoos came out clean!!!

The problem? Just days later, Beaty got sent packing to the Padres, one of L.A.'s most-hated rivals.

No word on how the fan is planning to move forward with the fresh tattoo now -- particularly because Beaty also changed his jersey number following the trade. But, Matt at least offered to somewhat help the guy out.

"Well, if he wants to scratch out the No. 45 and put in No. 27," Beaty said, "I'm happy to do that for him."

As for the whole ordeal, Beaty had a feeling the dude might come to regret it eventually.

"This guy sticks his arm with Cody’s [autograph], and he's like, 'Hey, sign my arm, too.' And I'm like, 'Sure,'" Beaty said.

"Then later that night, of course, I get notifications [of the tattoo] and I'm like, 'Geez, what is this guy thinking?' It's going to be with that guy for a long time."