THE son of late Holly­wood legend Dennis Hopper is caught up in an ugly rape scandal that threatens to torpedo his promising acting career.

Henry Hopper, 21, who has dated Lindsay Lohan and stars in the indie film “Tar” with James Franco and Mila Kunis, is reeling from al­legations that he sexually assaulted a 15-year-old girl after plying her with drugs and alcohol.

The unidentified teen’s mother filed a civil lawsuit against Hopper in Los Ange­les, alleging that the young actor “engaged in sexually offensive conduct” with the teen and “repeatedly [took] advantage of her youth and vulnerability.”

According to the court documents, the two met through a mutual friend in February 2011 and began communicating through Facebook.

In the months that followed, the suit says he invited the teenager to his Venice, Calif., home on sever­al occasions by promising her drugs and alcohol.

The suit claims the girl, who is now 16, required mental health treatment as a direct result of the assaults. The plaintiff seeks unspecified damages.

Hopper is the son of the late “Easy Rider” star and his fourth wife, Katherine La­Nasa. Before “Tar,” he appeared in Gus Van Sant’s “Restless,” which premiered at the Cannes Film Festival in 2011.

“This ugly rape scandal threatens to destroy Henry’s promising film career, but the victim’s family wants to make sure he never does this to an­other young woman,” a source close to the teen dis­closed.

There is no indication in­dication that the police were ever contacted about the alleged rape, and the Los Angeles County District Attorney has said the LAPD hasn’t contacted their office about the matter. But the source told The ENQUIRER that the allegations con­tained in the lawsuit could be just the tip of the iceberg.