FORTUNE — Mark King has quietly left KRG Capital, the Denver-based private equity firm he co-founded in 1996.

No word yet on King’s future plans, although there are rumors that he has formed another investment platform that includes former KRG investor relations pro Dale Meyer.

King’s portfolio companies have included Aurora Diagnostics, Case Logic, Chronic Care Solutions, Cetero Research, Liberty Dialysis and Marquette Transportation Co. Prior to co-founding KRG, he was a vice president with LM Capital Group and co-founded  Industrial Services Technologies.

KRG raised nearly $2 billion for its fourth middle-market buyout fund in 2007, but earlier this year delayed plans to raise a successor. That fourth vehicle had a 10.5% internal rate of return through Q3 2012, according to the University of California Regents. Its predecessor fund had a -5.8% IRR through the same time period.

Fellow KRG co-founder Bruce Rogers says that the departure occurred in late May and was based on “philosophical differences.” He added that KRG does not plan to begin raising its next fund until late 2014 or early 2015, despite having only around $350 million left in its current vehicle.

“We were slow getting out of the gates on Fund IV, and five of our portfolio companies are less than one year old,” he explains. “Our limited partners are supportive of our strategy and let us extend the investment period to seven years, and to nine years for add-on acquisitions.”

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