NEW YORK -- The Core Four is now down to We Three.

As many expected since the New York Yankees' 2010 season ended in disappointment in Texas, Andy Pettitte will officially announce his retirement at a news conference at Yankee Stadium at 10:30 a.m. ET on Friday.

Pettitte's intentions, first reported by 1050 ESPN Radio's Michael Kay, were confirmed by the Yankees in announcing the news conference.

Pettitte phoned Yankees owner Hal Steinbrenner to inform him of his decision, sources told ESPN The Magazine's Buster Olney.

"We thank Andy, his wife, Laura, and their family for their many contributions to this organization," managing partners Hank and Hal Steinbrenner said in a statement. "We hope the Pettitte family remains a part of the Yankees family for years to come, and we wish them nothing but the best moving forward."

Pettitte, who will turn 39 on June 15, has wrestled with thoughts of retirement for the past several seasons. But never had he seemed more serious about the imminent end of his career than last season, when he spoke several times about his desire to spend more time at home in Deer Park, Texas, with his wife and their four school-age children.

Pettitte's upcoming role as the star prosecution witness in the perjury trial of Roger Clemens, his former teammate and friend, may have also played a factor in his decision.