Diego Piacentini speaks at a news conference in Paris August 29 , 2000. Reuters | Charles Platiau

Diego Piacentini, one of the most senior executives at Amazon who had previously led its international business, has left the company after a two-year hiatus, adding to a string of executive departures over the past year. Piacentini, who went on a two-year leave in 2016 to work with the Italian government, has decided not to return to the company after his project came to an end in October, according to a person familiar with the matter. The Italy-born executive was considered one of CEO Jeff Bezos' top lieutenants during his 16-year tenure at Amazon, reporting directly to him and becoming part of his tight-knit group of senior leaders called the "S-Team." He joined Amazon from Apple, and reportedly drew the scorn of then-CEO Steve Jobs for joining a "boring retailer."

Piacentini was also one of the largest employee shareholders at Amazon. Before he left in 2016, he owned the third largest number of Amazon shares among all employees, after only Bezos and the retail group's CEO, Jeff Wilke, according to the company's 2017 proxy statement. The 79,146 shares he owned at the time would translate to roughly $122 million based on Monday's closing price. Piacentini previously hinted that he could come back to Amazon once his pro bono work with the Italian government was complete. In an interview with the Financial Times in September 2017, he said he planned to return to the e-commerce company, although he noted that "many things can change." During a Bloomberg interview this year, he declined to say whether he's returning to Amazon. It's unclear what his future plans are now. He didn't respond to a request for comment. Amazon declined to comment for this story. Piacentini joins a growing list of executives who have left Amazon this year, even as the company enjoys unprecedented success and a near-record stock price. At least 15 high-profile executives have announced their departures this year, an unusually high number for a company known for retaining its most senior executives for many years. Piacentini's departure is particularly notable given that he's the second S-Team member to leave Amazon this year, after Sebastian Gunningham, marketplace senior vice president, left in March. Bezos' S-Team, which reportedly contains fewer than 20 execs, is famous for seeing very little turnover historically, a part of Amazon's culture that the CEO once highlighted during an internal staff meeting. "I'm very happy that we don't have a lot of turnover on the S-team," Bezos said, according to a recording of a 2017 all-hands meeting that CNBC has heard. "I don't intend to change that — I like you guys a lot. I would expect any transition there to happen very incrementally over a long period of time."

Cashing in

Amazon's massive success has made it a popular poaching ground for executive talent. Many of the departed executives had more than a decade of experience building key parts of Amazon's business, and have joined hot start-ups or young public companies that would benefit from the adult guidance these experienced leaders could provide. In return, these people get fresh opportunities and a relief from the more bureaucratic culture of a big company. For example, Gunningham, who spent more than 10 years at Amazon, took the vice chairman role at WeWork. Greg Greeley, another highly regarded executive responsible for building the Prime membership program, left to join Airbnb in March. Tim Stone, former vice president of finance, is now Snap's chief finance officer. Other companies that recruited Amazon's executives this year include SoFi, Tesla and Robinhood.