Dr. Luke is firing back at Kesha’s attorney with a lawsuit … after he accused the high-powered producer of raping Lady Gaga — something Luke calls an “outrageous” lie.

After Lady Gaga told Howard Stern last week that someone in the music industry had raped her, Kesha’s lawyer Mark Geragos went on Twitter and asked, “Guess who the rapist was?”

When someone guessed Dr. Luke, Geragos responded, “#bingo.” TMZ contacted Geragos and he doubled down saying that he said it “because it’s true.”

Sr Luke has filed a defamation lawsuit, calling Geragos’ comment “maliciously false.” Gaga backed that up last week, telling TMZ it’s absolutely untrue that Luke was the mystery rapist.

In his docs, Luke also says he hadn’t even met Gaga at the time of the alleged rape 9 years ago — and adds he’s never been alone with her or touched her.