In a move that shocked investors, Walt Disney Co. Chief Operating Officer Thomas Staggs, the man widely believed to be the heir apparent to the entertainment giant's CEO post, announced his departure from the company Monday, effective May 6.

The 55-year-old Staggs was promoted to Disney's COO last year, basically making him the handpicked successor of current Chief Executive Officer Robert Iger. The 65-year-old Iger, who is credited for much of Disney's successes over the last few years, is set to leave the company in June 2018.

Despite leaving the company, however, Staggs announced that he would still remain employed as a "special adviser" to Iger. In a statement, the Disney CEO lauded Staggs for his contributions to the entertainment giant.

"Tom has been a great friend and trusted colleague for more than 20 years," Iger said. "He's made important contributions to this company, earning wide respect across the organization for his achievements and personal integrity. I'm proud of what we've accomplished together, immensely grateful for the privilege of working with him, and confident that he will be enormously successful in whatever opportunity he chooses." 

The COO's sudden departure did not sit very well with investors, sending the company's stocks plunging about 2 percent during Monday's after-hours trading.

Laura Martin, a Needham & Co. analyst who covers Disney, believes that Staggs' sudden departure was motivated by decisions of the company's board of directors.

"Tom Staggs is Wall Street's fair-haired boy," she said. "I think it is shocking that the board, after stringing him along, is doing this to him."

Despite his sudden departure, however, Staggs thanked Iger, who has been his mentor, and to Disney, which he served for years.

"Disney truly stands alone, not only because of the company's phenomenal creativity, but also because of the thousands of remarkable people who make it such an extraordinary place," Staggs said.

With Staggs' announcement, Disney will now have to find another person worthy to succeed the outgoing Iger. After all, during his tenure as the company's CEO, Disney experienced a number of transformative and, ultimately, lucrative changes. Iger led Disney through the acquisition of Pixar Animation Studios, Lucasfilm and Marvel Entertainment.

Thus, whoever is set to replace Iger as the head of the entertainment giant will have very big shoes to fill. Without Staggs, who was practically being groomed by the CEO to take over the company, Disney's future leadership is once more uncertain.