This ain’t no love story.

Tatum O’Neal has blamed half-brother Redmond’s shocking descent into a devil-horned suspected stabber on years of “horrifying and cruel” abuse by their late dad, Hollywood legend Ryan O’Neill.

The former child star gave her damning indictment after Redmond made a terrifying vision with horns tattooed on his head as he appeared in a California court charged with attempted murder.

“He’s doing very poorly, honey, very poorly,” Tatum, 62, told the Daily Mail of her troubled half-brother, the only child of Ryan O’Neal and Farrah Fawcett .

Remond O’Neal appeared in court with devil horns tattooed on his head last month. Frederick M. Brown for CA Post

“I love Red dearly, but he’s gotten heavy.…