As far as red flags go, Ronnie Spector’s tumultuous marriage to Phil Spector was the biggest and reddest of them all.

Phil was convicted in the 2003 murder of actress Lana Clarkson and died in prison last year. But before he was tried for the grisly crime, the relationship between the producer and his teenage protégé was marred by brutality, sick control and twisted love. And it ultimately wound up becoming a chilling harbinger of the violence to come.

Ronnie, the bad-girl vocalist of ’60s rock group the Ronettes, died Wednesday at 78 following a brief battle with cancer. But in the years preceding her death, the musician was open about her traumatic relationship with Phil, who first signed her band in 1963.

Phil would help bring Ronnie and the Ronettes chart-topping success with hit tunes from “Be My Baby” and “Baby, I Love You” (both 1963), to “The Best Part of Breakin’ Up” and “Walking in the Rain” (both 1964). The pair tied the knot in 1968, and the Ronettes called it quits shortly thereafter.

Ronnie’s reps didn’t respond to The Post’s request for comment.

In Ronnie’s 1990 memoir “Be My Baby: How I Survived Mascara, Miniskirts, and Madness,” she wrote that, while she admired her ex-husband’s musical genius, he was vindictive, controlling and violent.

In the book, she also mentions that he actually kept a gold coffin in their basement and told her he would kill her if she tried to leave him.

“I can only say that when I left in the early ’70s, I knew that if I didn’t leave at that time, I was going to die there,” she wrote.

The book further details how Phil kept her locked away in his California mansion, where he subjected her to harsh psychological abuse. In 1972, with the help of her mother, she made a run for it, barefoot, and barely escaped with her life.

Ronnie told People in 2018 about her mom’s aid and her ordeal: “She said, ‘I’m your mother and I’m telling you, we gotta get out of here. Or you, my little girl, are going to be gone.’”

The “Love On a Rooftop” musician continued, “It was so dark back in those days. Now I feel free now to be able to tell other women. Maybe not every woman will listen to me, but some will and I [hope] I can get one or two to save their [own] lives or save them from getting abused.”

As a result of their 1974 separation, Phil got custody of their three adopted kids — Donté Phillip and twins Louis and Gary. The record producer forced her to sign her life away in the divorce settlement and cut her out of future record earnings.

By that point, she had accused him of pulling a gun on her and reported that he had threatened to hire a hit man to murder her.

Decades after their divorce, Phil still felt as though he had some sort of control over Ronnie. He led a campaign in 2007 to bar her from being inducted into the Rock & Roll Hall of Fame.

“You’d think he might have focused on his murder trial,” the singer told The Post at the time.

The couple’s three adopted children also reportedly suffered abuse and trauma from the producer behind the Wall of Sound recording technique. Donté Phillip claimed in a 2003 Mail on Sunday interview that the trio was abused by Phil and described their relationship with him as a “thin line between love and hate.”

He also alleged that Phil trapped him and his brothers in their bedrooms “with locks on the door.”

When Phil eventually passed away at the age of 81, Ronnie spoke out about his death. “It’s a sad day for music and a sad day for me,” she wrote on social media at the time.

“When I was working with Phil Spector, watching him create in the recording studio, I knew I was working with the very best. He was in complete control, directing everyone. So much to love about those days,” she continued. “Meeting him and falling in love was like a fairytale. The magical music we were able to make together, was inspired by our love. I loved him madly, and gave my heart and soul to him.”

In perhaps the understatement of the century, Ronnie added that, although her ex was “a brilliant producer,” he was “a lousy husband.” She appeared to be at peace with the role he played in her career.

“Unfortunately Phil was not able to live and function outside of the recording studio. Darkness set in, many lives were damaged. I still smile whenever I hear the music we made together, and always will. The music will be forever.”