A rough day on Wall Street for Five9 shows how a CEO stepping aside can have big ramifications.

Five9’s Rowan Trollope

Chief executive officer Rowan Trollope announced his resignation from the cloud contact center software provider on Monday. The news immediately sent the company’s stock tumbling, down more than 22% as of 2 p.m. ET.

Trollope described the next stop in his career journey on Twitter: “I have resigned from Five9 and accepted a position as CEO of a venture backed pre-IPO startup.” He went on to say that “it has been an honor and privilege to serve our employees, our customers and our shareholders as we’ve quadrupled revenue and accelerated our growth rate.”

Trollope was at Symantec for 22 years and Cisco for six more before accepting the Five9 CEO job in 2018.

Old CEO Returns

Five9’s Mike Burkland

Former Five9 CEO Mike Burkland is returning to fill Trollope’s old position as CEO effective Nov. 28. Burkland resigned five years ago after a cancer diagnosis. Burkland is also chairman of the Five9 board of directors.

“I’m thrilled to resume the role of CEO and once again lead the amazing team at Five9 on our exciting journey ahead,” said Burkland. “When I was diagnosed with cancer in 2017, I resigned from the CEO post to focus on my health, while remaining very close to the business as chairman. Now, following successful treatments, I am pleased to report that my doctors have given me a favorable long-term prognosis. I’m so excited to get ‘back on the field’ with the Five9 team, which is a special, tight-knit group working passionately on the important mission of enabling our clients to reimagine their customer experience.”

Burkland went on to note that Five9 is “still in the early innings of the shift to the cloud.” But the company is “very well positioned in this massive market as we continue to execute on product innovation, our march up-market and international expansion.”

Burkland was CEO for nearly 10 years before stepping aside.

Today’s stock market fall aside, Five9 is bullish on its third quarter. The company now predicts revenue to be $198 million, beating its original guidance of $192.5 million-$193.5 million. Five9 will hold its earnings call on Nov. 7.

Zoom and Five9 made headlines last year when they appeared poised to merge in a deal worth nearly $15 billion. But Five9’s shareholders rejected the bid from Zoom in a move that ultimately doomed the transaction.