Legal question, if i own half a business..?

And my name is on the lease as 50% owner ( business registered as LLC) , but my partner sold his 50% to a guy without my knowledge and this guy came to the business saying he owns half of it and wanna ruin everything i did in the past six months and acting like a boss , what to do and how to deal with the situation? Is what my partner did was legal? if i called the police to remove the new guy, would he get to stay in the business if his name is not on the lease, just based on that bill of sale between him and my parner? I appreciate a legal answer for this especially people who know about this stuff, thanks