Wednesday’s news that Salesforce co-CEO Bret Taylor is stepping down appears to have been so sudden that even the CEO of Salesforce-owned Slack, and his circle of lieutenants, were taken by surprise.

Stewart Butterfield, CEO of professional chat service Slack, described Taylor’s departure as a negative and unforeseen development in an internal message to employees viewed by Fortune. “I’m sad about the news of Bret’s departure from Salesforce,” Butterfield wrote. “No way to spin this as a good thing, so I’m not going to try that.”

In the candid message, Butterfield gave accolades to Taylor’s years of hard work at Salesforce and explained that his executive team was even caught off guard by the announcement.

“I’ve been in an on-site with my exec team all day, and we were all surprised too. (That fact should not itself be too surprising: This is market-moving news, and therefore the group in the know was extremely small),” Butterfield wrote.

Salesforce shares were down roughly 10% in midday trading on Thursday, following the news of Taylor’s resignation, which was announced in concert with Salesforce’s quarterly earnings.

Taylor will remain at Salesforce through the end of January, after which he will leave the company and its board to focus on an unspecified “entrepreneurial” project.

Taylor is leaving after just one year in the co-CEO job alongside Salesforce founder and co-CEO Marc Benioff. In an interview with CNBC’s Jim Cramer on Wednesday, Benioff characterized Taylor’s departure as “a gut punch.”

Butterfield, a software entrepreneur who founded Slack and sold it to Salesforce last year for $27.7 billion, said in his internal note that the Slack executive team had to “pause to have a drink and commiserate” on learning the news about the leadership change. But he stressed that Slack’s plans would not change.

Butterfield also praised Taylor’s leadership, both at Salesforce and in his previous role as chairman of Twitter during Elon Musk’s chaotic takeover of the social networking company.

“It’s especially impressive when you factor in that he also had to deal with the insane bullshit at Twitter as chair of the board,” Butterfield wrote. “That fellow has enviable reserves of equanimity, poise, and patience.”

A Salesforce spokesperson could not immediately be reached for comment.