The Canada-based athletic wear company said on Monday in a regulatory filing that its CEO of four years, Laurent Potdevin, had resigned immediately, saying he “fell short” of Lululemon’s standards of conduct, without specifying what he had done, something likely to fuel the rumor mill and potentially harm the company.

“Lululemon expects all employees to exemplify the highest levels of integrity and respect for one another, and Mr. Potdevin fell short of these standards,” the company said in a statement.

Potdevin became CEO four years ago and after some challenges as many rivals such as Gap Inc’s Athleta and even Kohl’s, made big inroads into the so-called athleisure category Lululemon pioneered, the company signs more recently of renewed strength: last month it said it had had a very strong holiday season.

Early in his tenure, Potdevin had to contend with a founder-shareholder clamoring for a big shakeup in Chip Wilson. But on his watch, the company ultimately improved its supply chain, expanded its offering, made inroads with men and continued to thrive.

Lululemon Executive Chairman Glenn Murphy, a former CEO of Gap Inc (GPS), said “protecting the organization’s culture is one of the Board’s most important duties.”

The Vancouver company will look for a new CEO, and three senior executives got additional responsibilities: Celeste Burgoyne, EVP for the Americas, will handle stores and e-commerce; Stuart Haselden, Chief Operating Officer, will oversee finance, supply chain, staff, and technology; and Sun Choe, a merchant, will be in charge product development, design, innovation, and merchandising. Lululemon reaffirmed its expectation it will hit $4 billion in revenue in 2020.