EQT Corp. CEO Steven Schlotterbeck unexpectedly resigned on Thursday for “personal reasons” only one year after he took the helm of what is now the nation’s largest natural gas producer.

Company representatives offered no further comment, pointing instead to a statement from the board calling the 18-year EQT veteran a “valued contributor” for his role in overseeing the $8 billion acquisition of Rice Energy Inc. The acquisition created the country’s biggest gas producer with current volumes of roughly 4 Bcfe/d.

Schlotterbeck, 52, relinquished all of his EQT titles and has stepped down from the board. David Porges, who Schlotterbeck replaced one year ago, is to lead the company on an interim basis. Porges was serving as executive chairman and previously was CEO for about seven years.

Schlotterbeck took the torch from Porges after a series of acquisitions. The company has acquired more than 400,000 acres in the Appalachian Basin since 2016, including the marquee purchase of Rice, which Schlotterbeck engineered and completed amid a shareholder revolt of sorts as some investors viewed the Rice deal as pricey and pushed the company to generate more value.

After the Rice transaction, Schlotterbeck put forward a plan to separate the midstream and production businesses in a complex tax-free spin-off expected to close in 3Q2018. The separation would also create the third largest gas gatherer in the country, according to EQT.

“EQT is at an important transition point, and we are confident that the company is well positioned to advance its strategy while implementing the previously announced separation plan,” the board said. “With the support of a strong and dedicated team, the company is making solid progress and remains on track to complete the spinoff by the end of the third quarter 2018.”

Schlotterbeck held various engineering and management positions with EQT until 2008, when he was promoted to vice president and president of exploration and production. When the succession plan was announced in October 2016, Poges called it seamless, “thanks in large part to the way in which Steve has steadily embraced increasing levels of responsibility at EQT.” Schlotterbeck had pitched himself as a steady hand to guide the company through the next era of unconventional development.

EQT’s stock tumbled after the announcement on a day when the broader market fared better. EQT fell more than 5% on Thursday to close at $49.73/share.