(Bloomberg) -- A senior executive at Flow Traders NV, Europe’s biggest market maker in exchange-traded funds, left the firm amid an internal investigation into alleged incidents at a company party in a Swedish ski resort, people familiar with the matter said.

Thomas Wolff, who was chief technology officer at Amsterdam-based Flow Traders and a member of its management board until March, is at the center of the review, the people said. The alleged incidents took place that month at the Copperhill Mountain Lodge in the town of Are where dozens of Flow Traders employees had gathered for the firm’s annual party, according to the people, who requested anonymity as details aren’t public. 

At a costume party thrown after a day’s skiing, Wolff allegedly struck a male colleague who was dressed as former U.S. President Donald Trump and then allegedly groped a female colleague, the people said. The episode is now under internal review following complaints, according to the people. 

The alleged episode comes just months after Flow Traders ousted its top U.K. executive following an incident in a London pub. Christopher Meyers left after allegedly engaging in unprofessional behavior toward female employees at BlackRock Inc., Bloomberg reported in January. The New York-based asset-management behemoth is a key business partner for the Dutch firm.  

Laura Peijs, a spokeswoman for Flow Traders in Amsterdam, declined to comment. Wolff didn’t respond to multiple requests for comment.  

Wolff joined Flow Traders in 2009 and he rose to lead its technology operations. In 2018, he joined the Amsterdam-based firm’s five-member management board.

On March 18, Flow Traders announced that Wolff was leaving the management board “due to personal circumstances” and intended to “spend some time away in Germany for the next few months.” However, he remained part of the firm’s “core leadership team as we focus on building our technology capabilities and roadmap beyond 2022,” Chief Executive Officer Dennis Dijkstra said in the statement. 

But early last month, a few days after the Are trip, Wolff sent a note to colleagues saying he would no longer be returning to Flow Traders, according to an email seen by Bloomberg. He cited a wish to spend more time with his family and apologized for “hassles caused,” without elaborating. 

Flow Traders, founded in 2004, has become a key player in the market for exchange-traded funds, the hugely popular, publicly traded entities that invest in baskets of stocks, bonds and other assets. European ETFs have about $1.4 trillion under management, according to Bloomberg Intelligence data.  

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