Six Flags Entertainment announced Tuesday morning that the company’s president and CEO, John Duffey, had suddenly retired nearly a year and a half after being named to the position.

He has been replaced by his predecessor, Jim Reid-Anderson, who has been serving as executive chairman since February 2016. Prior to that, Reid-Anderson was chairman, president, and CEO dating back to August of 2010.

The Texas-based regional theme park company gave no reason for Duffey’s departure; an email to Stephen Purtell, senior vice president of investor relations, was not immediately returned. Before he was named CEO last year, Duffey had been the company’s chief financial officer since September of 2010.

“I do want to wish John all the very best for the future and to thank him for his major contributions during his excellent tenure with the company, including his time as president and CEO,” Reid-Anderson said in a statement.

Shares were down more than two and a half percent midday Tuesday, and early reaction outside the company seemed to be one of bafflement.

The headline of an investor note from Stifel Nicolaus analyst Steven Wieczynski said: “Is the Abrupt CEO Change Shocking? Yes! Do We Believe it’s a Fundamental Issue? No!”

Wieczynski wrote that he spoke to the company early Tuesday and learned that Duffey was already gone from the company and there was no transition period.

“In our view, something strange is going on although our most important takeaway is nothing is wrong with the company from a fundamental standpoint,” he wrote. “We asked the company about the timing around Mr. Duffey’s ‘retirement’ and it seems it is not a health issue but the company would not comment on it more than that.”

Wieczynski wrote that the incoming CEO stands by long-term goals of reaching earnings targets of $600 million this year and $750 million by 2020. Duffey, he said, would still get part of his incentive compensation tied to those goals.

In the official announcement, Six Flags said that the board of directors had appointed Reid-Anderson to the CEO position due to Duffey’s retirement.

Last year, when Duffey was named to the top job, Six Flags said it was splitting executive leadership roles by making Reid-Anderson executive chairman and Duffey president and CEO. Tuesday’s announcement indicates those roles are no longer split, as Reid-Anderson’s title is once again chairman, president, and CEO.

“Six Flags is the leading regional theme park company in an extremely attractive industry, and we have significant global growth opportunities in the short, medium and long term,” Reid-Anderson said in a statement. “I am very proud and excited to rejoin the operating team and look forward to executing our business strategy. We have had seven record years in a row and I believe that the best is yet to come.”

Six Flags, which releases quarterly financial results next week, has 20 parks in the U.S., Mexico, and Canada, and has deals in place for international expansion to countries including China and Dubai.

Photo Credit: Six Flags replaced CEO John Duffey with former CEO Jim Reid-Anderson. Duffey is pictured here in an image from an interview with CNBC. CNBC