Yep, LeBron James is now a part-owner of one of the most storied franchises in pro sports ... the Boston Red Sox.

So, how did it happen?

LeBron has obtained shares in the Fenway Sports Group -- which is the parent company of the BoSox, along with several other prominent sports teams and companies.

No word on how many shares LeBron owns or how much money he put down -- but what's clear is he's a minority partner in FSG, which means he's a part-owner of the Sox, as first reported by the Boston Globe.

By the way, the Boston Globe is owned by John Henry -- the majority owner of the Boston Red Sox, who's reportedly worth $2.8 BILLION.

LeBron has publicly supported the NY Yankees for years -- but obviously, those days are over now.

The rivalry between NY and Boston goes back decades and there's no way you can support both teams ... even if you're LeBron!

LeBron's business partner, Maverick Carter, is also part of the FSG ownership group now -- which makes him a Sox part-owner as well.

LeBron has yet to publicly comment on the deal -- but he's expected to make some sort of announcement in the near future.

FYI, the Boston Red Sox are reportedly valued at $3.3 BILLION, according to Forbes ... which makes them the 3rd most valuable franchise in MLB, behind the Yankees and Dodgers.

LeBron has some experience with pro sports ownership -- he bought a piece of the legendary Liverpool soccer team back in 2011.

As for FSG, the company owns pieces of the NESN network, Roush Fenway Racing, Liverpool FC and more.

The move expands LeBron's already impressive empire -- he's reportedly made $343 million from NBA contracts alone.

Plus, his media company, Springhill Entertainment, is thriving with "Space Jam 2" coming out soon.

And, don't forget that reportedly $1 billion lifetime deal with Nike.

He's also a part-owner of the Blaze pizza company and has a stake in the Ladder supplement company, which he created with Arnold Schwarzenegger.

Bottom line ... LeBron is not only the greatest athlete on the planet, he's a pretty savvy businessman, too!