"It is with an incredible sense of gratitude and humility — and, I must admit, a bit of amazement — that I write to you this evening with the news that I am returning to The Walt Disney Company as Chief Executive Officer," Iger wrote in an email to employees, obtained by CNBC. 

Shares of Disney surged 13% in premarket trading following the surprise news. Shares are down more than 41% year-to-date (as of Friday's close).

Iger, 71, who spent four decades at Disney, including 15 as the CEO, "has agreed to serve as Disney's CEO for two years, with a mandate from the Board to set the strategic direction for renewed growth and to work closely with the Board in developing a successor to lead the company at the completion of his term. Mr. Iger succeeds Bob Chapek, who has stepped down from his position," Disney wrote in a press release. 

"The Board has concluded that as Disney embarks on an increasingly complex period of industry transformation, Bob Iger is uniquely situated to lead the company through this pivotal period," Susan Arnold, Chairman of the Board, wrote in a statement.