FORTUNE — Jim Kester has stepped down as head of private equity investing for the Abu Dhabi Investment Authority, Fortune has learned.

No one knows exactly how much money is managed by ADIA, a sovereign wealth fund, but recent estimates have been around $600 billion. Between 5% and 10% of that is allocated to private equity, including investments in private equity funds and co-investments with those funds.

Kester joined ADIA in late 2010 after having spent four years running private equity out of New York for Zurich Alternative Asset Management. Before that he was with Allianz Private Equity Partners in Germany.

A source familiar with the situation said that Kester gave notice earlier this month, but was not aware of his future plans.

Kester would only say “no comment” when reached earlier today via phone, and ADIA did not return Fortune’s calls.

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