Apple chief financial officer Peter Oppenheimer will retire at the end of September, after 18 years at the company. Luca Maestri, Apple's vice president of finance and corporate controller, will become his successor. The role will begin to transition to Maestri in June. "Luca has over 25 years of global experience in senior financial management, including roles as a public company CFO, and I am confident he will be a great CFO at Apple," Apple CEO Tim Cook says in a statement.

Maestri came to Apple about a year ago from Xerox, where he served as CFO. Apple appears to have known about Oppenheimer's retirement plans for some time now, and it says that Maestri was always intended as his replacement. "When we were recruiting for a corporate controller, we met Luca and knew he would become Peter’s successor," Cook says. Maestri previously spent two decades with GM, holds a bachelors in economics from Luiss University in Rome, and a masters in Science of Management from Boston University.

Though he's only been at Apple for a year, Maestri already appears to have had a large impact on its finances. In particular, Maestri is believed to be one of the driving forces behind Apple's recent and uncharacteristically large stock buybacks. The company's buyback program has become increasingly aggressive since Maestri came on board, and investors estimate that Apple will repurchase over $30 billion in stock this year.

While Apple stresses that it's prepared for the transition, it'll be a big change to its executive team: Oppenheimer joined Apple in 1996 and became its CFO eight years later. During the decade that followed, Apple experienced the largest growth and success in its history, fueled first by the iPod, then the iPhone and iPad. His departure is one of only a few to Apple's executive team since the death of Steve Jobs in 2011. That list includes retail chief Ron Johnson who left to briefly run JCPenney, and iOS software chief Scott Forstall, who was removed from the company during a reorganization in late 2012.

As Cook notes, Oppenheimer has overseen much of Apple's major growth. "Peter has served as our CFO for the past decade as Apple’s annual revenue grew from $8 billion to $171 billion and our global footprint expanded dramatically," he says. Cook emphasized that Oppenheimer has put together a "professional succession plan" to ensure that the transition won't cause problems for Apple. Certainly, with several months to begin the transition, Oppenheimer should have plenty of time to ease Maestri into the new role.

Oppenheimer was recently added to Goldman Sachs' board of directors, though his stated plans for retirement are all personal. Oppenheimer says that he wants to travel, spend more time with his family, and get a pilot's license.

Josh Lowensohn contributed to this report.