GM Korea’s announcement late yesterday that CEO’s Michael Arcamone is leaving the company caught many colleagues unawares.

The auto maker in a statement says Arcamone is retiring from General Motors after 22 years. The announcement was sudden and took everyone by surprise, a company spokesman tells WardsAuto.

Tim Lee, president of GM International Operations in Shanghai, says in a statement that John Buttermore will serve as an interim president and CEO.

Buttermore joined GM in 1978 and previously has held positions as GM North America vice president-labor relations and GM Powertrain vice president-global manufacturing. He currently is headquartered in Shanghai, where he is serves as GMIO vice president-manufacturing, a position he has held since September 2009.

Arcamone will remain in Korea through the end of January before moving back to his native Canada, the spokesman says.

Arcamone replaced Michael Grimaldi as president and CEO in 2006 and oversaw the renaming of the auto maker from GM Daewoo Auto & Technology to GM Korea last year.

It was a large undertaking that included the rebranding of all vehicles manufactured by the Korean subsidiary from Daewoo to Chevrolet as of March 2011 and the introduction of eight new models.

Arcamone simultaneously held the post of chairman of the supervisory board of General Motors Powertrain Uzbekistan and spent much time overseeing GM operations in that country.

Buttermore will commute between Shanghai and GM Korea headquarters in Bupyeong, a 1-hour flight, the spokesman says. He will continue to oversee GM’s manufacturing operations in the Asia/Pacific region and maintain oversight of GM business operations in Africa and Southeast Asia.