Kevin Mayer, Disney’s most senior executive in charge of streaming, is leaving the company to become CEO of TikTok, the short video sharing app. Mayer resigned on Monday.

The New York Times reports that Mayer will act as chief operating officer of TikTok’s parent company ByteDance.

TikTok is that rare Chinese owned digital company that has moved beyond its home country to have major success in the West. The app has been downloaded 1.9 billion times according to the Times, a phenomenally high number. It has appealed to a generation brought up on Snapchat, and the generation before it that remembers the art of Vine.

Mayer told the Times: “I was happy with my job at Disney [but] the magnitude of this opportunity was just something I couldn’t pass up.”

In the context of his Disney career, Mayer has helped lead the company’s Disney+ streaming service that had a very successful launch late last year. Earlier he was also instrumental in helping the company acquire huge firms like Pixar, Lucasfilm and the Marvel franchise, the building block of the Disney+ service aside from Disney’s own vault of content.

Many viewed him as the logical successor to Bob Iger, the former CEO who stepped down recently. But Iger was replaced by Bob Chapek, Disney’s chairman of theme parks. Mayer, it seems, saw it as time to move on.

“Kevin has had an extraordinary impact on our company over the years,” Chapek said in a statement. “Having worked alongside Kevin for many years on the senior management team, I am enormously grateful to him for his support and friendship.”