Just a year after being acquitted on charges of soliciting a minor for child pornography, Kelly, 42, is again under investigation for allegedly being sexually involved with an underage girl, The ENQUIRER has learned exclusively.

On June 16, detectives showed up at Kelly’s home in Olympia Fields, Ill., after receiving a tip that an underage girl was staying with him, a family insider revealed.

Neither Kelly nor the girl were at the house when police arrived, but authorities were able to locate the girl and determined that she is 17 – the age of legal consent in the state. But cops are now looking into how long the relationship has been going on "so they can establish if they were involved before she turned 17," says the insider.

Detective Michael Mayden of the Olympia Fields Police Department confirmed to The ENQUIRER that the investigation is ongoing, but no complaint has been filed. The detective says Kelly will be interviewed by police when he returns to Illinois after his current tour in South Africa.

"I plan to talk to (Kelly) then and make a determination at that time if there is anything to pursue or not," said Detective Mayden.

Kelly has a long and troubling history with underage girls. In 1994, he reportedly married his underage protege, Aailyah, when she was 15 years old. The union was quickly annulled when rumors began to surface in the media.

In June 2002, he was indicted on 21 counts of having sex with a minor after a sex tape was released that featured a man who appeared to be Kelly having sex with a 14-year-old girl. The charges were later reduced to soliciting a minor for child pornography.

A Chicago jury found him not guilty in June 2008.