CHICAGO — It seemed for a while as if R. Kelly’s day in court might never come.

But after six years of repeated delays, jury selection is set to begin Friday in the Grammy-winning R&B singer’s trial on child pornography charges, prompted by a videotape allegedly showing Kelly having sex with a girl as young as 13.

Prosecutors, though, will have a unique challenge: The alleged victim, now 23, says it wasn’t her. And Kelly’s attorneys — including Ed Genson, who often represents the rich and famous — haven’t admitted it’s Kelly in the video.

“How is there not reasonable doubt when the two people say it’s not them?” said Michael Helfand, a Chicago attorney not involved in the case.

But Helfand conceded that it’s unclear what supporting evidence the prosecution might present.

The 41-year-old Kelly, whose first name is Robert, faces up to 15 years in prison if convicted. But Kelly — one of urban music’s biggest stars, and a consistent hitmaker despite his legal woes — is glad the wait is over, his spokesman said.

“Every waking moment, he’s always had this hanging over his head,” spokesman Allan Mayer said. “He’s confident that when all the evidence comes out he’ll be shown not to be guilty of any crime.”

The centerpiece of the trial is likely to be the video footage, which Judge Vincent Gaughan ruled may be shown in open court.

Prosecutors claim the videotape was made sometime between Jan. 1, 1998 and Nov. 1 2000, and that the girl was born in September 1984.

Kelly was indicted on pornography charges June 5, 2002, after the tape surfaced and was sold illegally on street corners and the Internet. Chicago police began investigating after receiving the tape from the Chicago Sun-Times, which said it was sent to the paper anonymously.

Police and prosecutors said their investigation, including interviews with about 50 witnesses, determined Kelly and an underage girl were on the tape, and that FBI forensics experts had determined the tape was authentic.

Prosecutors may need more than a videotape to prove their case, said Helfand, the Chicago attorney.

“I’d be beyond surprised if he got convicted based on what’s out there,” said Helfand.

It is unclear whether prosecutors have asked — or would be allowed — to tell jurors about accusations that Kelly allegedly had sexual relations with other minors, because some of the trial proceedings have been kept secret by the judge. Media outlets, including The Associated Press, have filed a legal challenge seeking to get court records and hearing transcripts unsealed.

Kelly has settled three lawsuits accusing him of having sex with underage girls, filed in 1997, 2001 and 2002. In the third suit, the woman claimed that she began having sex with Kelly when she was 16, and that he forced her to have an abortion.

In 2003, Kelly was arrested in Florida on child pornography charges after investigators said they found photos of him having sex with a girl. Charges were dropped after a judge ruled detectives illegally seized the photographs from a digital camera in his home.

Documents show Kelly secretly married the singer Aaliyah in 1994, when she was 15. The marriage later was annulled by her parents; Aaliyah died in a plane crash in 2001.

The trial’s six-year gap from indictment to trial is uncommon in child porn cases. But while suspects have a right to demand a swift trial, they’re not obligated to ask for one, especially if they calculate that speed isn’t in their best interests.

In Kelly’s case, more than 30 pretrial motions contributed to delays. At one point, hearings were delayed when Judge Gaughan fell off a ladder at home and suffered multiple fractures. By the time he recovered, Kelly needed emergency surgery for a burst appendix.

Despite his legal troubles, Kelly — who rose from poverty on Chicago’s South Side to become a superstar singer, songwriter and producer — still retains a huge following, and his popularity has arguably grown since being charged in 2002. The singer has released more than half a dozen albums, most of them million-sellers. He’s also had a multitude of hits and gone on tours. His campy video series “Trapped in the Closet” have a cult following so strong that the Independent Film Channel premiered the latest chapters of the farcical musical, out on DVD, on its web site last year before showing them on the network. Kelly has a new song, “Hair Braider,” out now, and is due to release a new album in July.

Although he won a Grammy in 1997 for the gospel-like song “I Believe I Can Fly,” his biggest hits are sexually charged songs like “Bump N’ Grind,” “Ignition” and his current single.

The trial is expected to draw crowds of reporters and fans to the courthouse. But Gaughan is expected to keep a tight rein on the proceedings, from which cameras, cell phones and recorders are banned.

When a fan snapped a picture of Kelly with her cell-phone camera during a pretrial hearing last year, Gaughan sentenced her to five days in jail and ordered her phone destroyed.

“He’s not one of those guys who’s going to let this trial turn into a circus,” said Helfand.