For decades, it was one of the music industry’s most disturbing open secrets: R&B singer R. Kelly was hounded by sexual misconduct allegations, often involving minors, but continued to enjoy the spoils of stardom.

But Friday saw a moment many were skeptical would ever come. Illinois prosecutors outlined charges that Kelly abused four victims, three of whom were between 13 and 16, for a total of 10 counts of aggravated criminal sexual abuse from 1998 through 2010. Each count carries a possible sentence of three to seven years. Cook County State’s Attorney Kim Foxx announced the charges at a Friday afternoon news conference and Kelly turned himself in later that evening.

Foxx offered no further comment on the case.

Over the years, the 52-year-old singer, best known for his hits “I Believe I Can Fly” and “Bump n’ Grind,” left a trail of settlements with teenagers he allegedly sexually assaulted.

In 2002, he was charged with child pornography after a graphic videotape was turned over to a Chicago Sun-Times reporter and later the police. Kelly, whose given name is Robert, was eventually acquitted and continued his chart-topping career but finally started to see public backlash in the #MeToo era.

Renewed interest in his behavior peaked with a ratings-grabbing docuseries, “Surviving R. Kelly,” which aired on Lifetime last month. Fallout from the series led his longtime record label, Sony, to finally drop him, while Foxx put out a call for victims of the singer to come forward to aid in possible prosecution.

“R. Kelly has never admitted what he’s done,” filmmaker dream hampton, the executive producer of the series, said Friday. “It infuriates me that so many of his fans and so many black people have been willing to forgive him for something for which he’s never shown any contrition. I hope this time the courts get it right and he pays for his almost three decades of harm.”

Steve Greenberg, Kelly’s attorney, called the charges “old regurgitated stuff” when approached by reporters Friday outside the singer’s studio.

“They’re making him a sacrificial lamb for their own sake and there’s no merit to any of this,” he said.

Friday’s announcement pleased Asante McGee, 39, who ended what she termed an abusive two-year relationship with Kelly in 2016. She is glad Kelly is facing charges but says she’s concerned about the young women in their early 20s who remain with him. The parents of those women, who met Kelly in their teens, were highlighted in the Lifetime special and one of the couples, Timothy and JonJelyn Savage, are part of a separate investigation of Kelly in Fulton County, Ga.

The Savages have said their daughter is being held against her will. Kelly has denied that.

“It’s a victory and it’s also a sad day because I’m concerned for the safety of those girls,” McGee told The Post. “I’ll be celebrating once I know those girls are safe.”

Kelly was indicted once before, in 2002, on child pornography charges after authorities received a videotape that allegedly showed the singer with a girl introduced to him when she was 12. But the girl alleged to be in the video chose not to testify and, as jury foreman Jamon Mytty told The Post last year, that led to Kelly’s acquittal when the case went to trial in 2008.

“I think we all agreed it was certainly him in the video,” Mytty said. “But without any kind of testimony from her or her parents, you had enough reasonable doubt to say, ‘We don’t know for sure.’ ”

Long before his child pornography case, allegations against Kelly were a topic of conversation within the music industry. As early as 1994, his tour manager warned the top executive at Jive Records.

“Clearly, we missed something,” Jive founder Clive Calder told The Post last year.

By the time Calder sold his music company in 2002 for $2.7 billion, Kelly had already settled multiple cases, requiring women to sign nondisclosure agreements. He had also illegally married his 15-year-old protege Aaliyah in 1994, when he was 27. The marriage would be annulled the following year. Aaliyah died in a plane crash in 2001.

Kelly preyed on young singers who he promised to help with their careers, according to a group of women interviewed for an investigation by The Post last year. The live-ins were expected to follow his rules, which included calling him “Daddy,” eliminating all social media and cutting off contact from family and friends, the women said. The rules were so strict, they said, that they were told they had to text either Kelly or an assistant to leave their rooms. When he was busy in the studio, that could mean leaving them stuck in backrooms, hungry and forced to urinate into cups.

Still, even after the trial and the continued rumors about his behavior, he remained a commodity. Kelly had six No. 1 albums to his credit and was something of a singular pop culture figure, known for being both the man responsible for songs such as “I Believe I Can Fly” and the punchline in a popular “Chappelle’s Show” sketch that directly addressed the videotape at the center of his court case. This decade, he recorded duets with A-list stars Lady Gaga (in 2013) and Chance the Rapper (in 2015) and remained on Sony subsidiary RCA Records until January.

What remained consistent throughout Kelly’s career was the presence of Jim DeRogatis, the former Chicago Sun-Times reporter who first wrote about Kelly’s behavior in 2000 and remained the most regular chronicler of his alleged misdeeds, including a major story for BuzzFeed in 2017. On Friday, he was in attendance at the Chicago news conference announcing the charges.

Kenyette Barnes, co-founder of the #MuteRKelly movement, said she was feeling confident after the indictment.

“Right now, I feel like we have just reached a point of reckoning,” she said. “This is the culmination of years of activism and years of survivors coming forward and demanding accountability.”

Bethonie Butler and Sonia Rao contributed to this report.