Shares of cloud software vendor Five9 closed down 25% Monday and fell to their lowest since March 2020 after CEO Rowan Trollope announced his resignation.

Trollope is leaving to become CEO of a venture-backed pre-IPO startup, he said on Twitter. He is being succeeded by former Five9 CEO Mike Burkland, who resigned as CEO in 2017 after he was diagnosed with cancer. Burkland will replace Trollope effective Nov. 28.

“It has been an honor and privilege to serve our employees, our customers and our shareholders,” Trollope wrote in a tweet.

Five9 provides contact center software that aims to help agents offer more effective service over the phone and from any location. Zoom agreed to acquire Five9 in mid-2021 in an all-stock purchase valued at $14.7 billion, after shares of both companies soared during the pandemic with people across the country working from home.

However, Five9 shareholders were not satisfied with the small premium that Zoom was set to pay, and they ultimately rejected the deal. Investor appetite for cloud stocks has plummeted since then as rising interest rates and inflationary concerns coupled with the reopening of many offices has changed the industry’s near-term trajectory.

Five9 has lost more than 70% of its value since the stock peaked in August 2021. Zoom is more than 85% below its record reached in late 2020.

Trollope, who was a top executive at Cisco before taking the Five9 job in 2018, said the company is still in a “great position,” and he remains bullish on its ability to “tackle the future.”

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