Singer R. Kelly had to postpone his book launching party tonight in New York for a mysterious “health emergency,” according to TMZ.

A representative of R.Kelly said the singer has to officially move the event to a later time “due to a health emergency that has sidelined Mr. Kelly in Chicago.” The rep did not disclose any information about the illness but added, “We sincerely apologize for any inconvenience this has caused.”

His rep adds that it’s “unclear how long Kelly may be sidelined.”

Sources report The “Trapped in the Closet” creator underwent surgery in July 2010, after being rushed to Chicago’s Northwestern Memorial hospital. In a message to fans the following month, he shouted out all the “prayer warriors” in his corner.

“The doctor said the surgery went well,” Kelly added of his hospital visit last year. “I know it may not look like it, but it did. I want y’all to continue to pray for me. Be strong out there, I will be back. I know it’s a lot of negativity out there, please don’t believe the hype. God is good all the time.”

In addition to his upcoming memoir, R. Kelly is also promoting his 11th studio album,Write Me Back, which debuted this week.