It's a case of too bad, so sad for Alec Baldwin ... according to the art gallery owner he's suing for selling him a "fake" painting.
Mary Boone responded to Baldwin's suit, saying the actor waited more than 6 years to file the suit over "Sea and Mirror" -- the Ross Bleckner painting Boone's gallery sold him for $190k. In docs, Boone's legal team says the statute of limitations has run out, so Baldwin's got no beef ... legally speaking.
Further, she claims Baldwin committed tax fraud. Boone's attorneys claim he should have paid $16,625 in NY city and state tax on the painting, but instead had it "shipped momentarily" to his Cali home, then back to his NYC pad.