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Chicago, IL (SportsNetwork.com) - Jon Lester has officially reunited with Theo Epstein.

On Saturday, the Chicago Cubs announced a deal with Lester, who reportedly agreed to a six-year contract worth $155 million. He will be formally introduced by the Cubs at Spiaggia restaurant in downtown Chicago on Monday.

The 30-year-old Lester went 6-4 with a 2.35 ERA for the Oakland Athletics after he and outfielder Jonny Gomes were acquired in a blockbuster trade- deadline swap from the Red Sox for outfielder Yoenis Cespedes.

The southpaw went 16-11 with a career-best 2.46 ERA in 2014.

Lester is most known for his prowess in the postseason, where he is 6-4 with 2.57 ERA in 14 career appearances, including a perfect 3-0 mark with a sparkling 0.43 ERA in the World Series.

Lester has a 116-67 record with a 3.58 ERA over his nine-year career.

He turned down a $70 million contract extension from Boston during the spring, the team which he helped win two World Series titles.

Epstein became the youngest general manager in MLB history when the Red Sox hired him following the 2002 season and helped them win a pair of World Series prior to becoming the president of baseball operations for the Cubs in 2011.