Charlie Sheen Dragged Into Mueller Lawsuit

Charlie Sheen just can't escape the grip of the Mueller family drama ... he's now caught in the middle of a nasty lawsuit his former mother-in-law filed over the purchase of Charlie's house.

According to legal docs obtained by TMZ ... Charlie is being subpoenaed to testify in a lawsuit filed by Brooke Mueller's mom, Moira Fiore, who claims she was screwed out of her commission by Charlie's real estate agent.

But here's the twist. Charlie will be subpoenaed not by Moira, but by the agent, Marty Trugman. Moira claims Charlie gave her authority to find a house, and she tapped Marty as the agent when he promised to give her 25% of his commission. He didn't ante up .... he tells TMZ he promised her zilch.

And the plot thickens. Both Moira and Marty have named Brooke as a key witness, but she's a drug addict so her credibility is shaky, to say the least.