Hollywood power couple Blake Lively and Ryan Reynolds are being targeted in a $400 million defamation suit by Justin Baldoni, Lively’s co-star on bleak romance “It Ends With Us” — the latest caustic twist in the legal battle engulfing the film.

The suit from Baldoni, who also directed the film, comes weeks after Lively filed a sexual harassment complaint against him, protesting her treatment on set, and then a lawsuit accusing him of launching a retaliatory media campaign against her.

The war between the stars was dragged into the spotlight when fans noticed during promotion of the film that they did not follow one another on social media.

It soon emerged that Lively had complained of Baldoni’s behavior on the set, accusing him of — among other things — speaking inappropriately about his sex life and seeking to add intimate scenes into the film that she had not previously agreed to.

Lively also said lead producer Jamey Heath had watched her while she was topless, despite having been asked to turn away.

Then, Lively alleges, Baldoni ignited a PR campaign to smear her and divert attention away from complaints she might make about the men’s alleged actions.

Baldoni also sued The New York Times after it published a piece into that alleged smear campaign, including what it said were emails and texts discussing the media outcry.

Baldoni countered in the newly filed court documents that Lively hijacked the production of “It Ends With Us” and that she defamed him and, with Reynolds, sought to extort him.

“Plaintiffs now have no choice but to fight back armed only with the truth — and the mountain of concrete evidence disproving Lively’s allegations,” the lawsuit alleged.

“Heartbreakingly, a film that Baldoni envisioned years ago would honor the survivors of domestic violence by telling their story, with the lofty goal of making a positive impact in the world, has now been overshadowed beyond recognition solely as a result of Lively’s actions and cruelty.”

The film, based on the book by Colleen Hoover, touches on issues of domestic violence and abuse.

Baldoni’s attorney Bryan Freedman added in a separate statement that “Lively will never again be allowed to continue to exploit actual victims of real harassment solely for her personal reputation gain at the expense of those without power.”