Alex Navab — a dealmaker who had once been a leading candidate to succeed billionaire Henry Kravis at buyout firm KKR & Co. — died on Sunday at age 53.

Navab died while on vacation with his family, his firm Navab Capital Partners said in a statement on Monday, without providing further details.

It wasn’t the first sign of possible health issues for Navab. In 2013, he was co-head of North American private equity at KKR when he collapsed during the annual meeting of fund investors.

Navab may have died if he hadn’t been revived by the personal security team of KKR co-founder George Roberts, which was trained in CPR.

Navab was diagnosed with cardiac arrhythmia, according to one source.

A KKR spokesperson at the time said, “Alex is in excellent health.”

Others, however, believed the incident put Alex out of contention to run KKR.

In 2015, Navab, as a member of KKR’s management committee, said at a conference that he was helping Kravis choose a successor, a signal to some that he was out of the running. At the time, a KKR spokeswoman called that an absurd interpretation of his comments.

Still, Navab left KKR in 2017, forming Navab Capital Partners. KKR named Joseph Bae and Scott Nuttall as co-presidents and, essentially, the future heads of the firm.

Navab Capital said in a Monday statement, “It is with deep sadness that we share the news of the untimely passing of our founder.”

“We are heartbroken,” KKR founders Henry Kravis and Roberts said in a Monday statement.

“Alex was an outstanding investor, leader, mentor and a friend to many,” a company spokesperson said.

Navab joined KKR in 1993 and was on the boards of companies including Nielsen Holdings.