In his first interview since Musk took Twitter private in a landmark $44 billion deal, Williams told Bloomberg’s The Circuit With Emily Chang that he originally believed the notion of Musk taking over Twitter was “interesting and fun.”

However, he revealed, by the time the deal closed, his stance had changed, and he was in fact “sad when the purchase actually went through.”

After attempting to pull out of the acquisition, citing concerns over the number of bot—or fake—accounts on the platform, Musk, the world’s wealthiest person, eventually decided—under legal pressure—to buy the company.

Williams, who was Twitter CEO between 2008 and 2010, is no longer a Twitter shareholder, but as one of the company’s first stakeholders has been closely watching the drama around the Musk-led Twitter unfold.

“I don’t think he’s dialed it in quite right yet,” Williams said of Musk in the interview, which aired Thursday night. “I think he’s brilliant. But no one’s brilliant on everything.”

Musk under fire

Musk, who said he wanted to buy Twitter so that he could make the social network “a platform for free speech,” has come under fire for how he’s been running the company since the deal closed late last year.

Under his stewardship, Twitter has faced accusations of becoming a “far-right social network,” seen its value plummet by two-thirds thanks largely to fleeing advertisers, and lost four in five workers either through mass layoffs or voluntary resignations. The site itself has suffered a slew of technical problems, including during the recent launch of divisive Florida Gov. Ron DeSantis’s presidential campaign.

This week saw Musk step down as CEO of Twitter to be replaced by Linda Yaccarino, former advertising chief at media giant NBCUniversal, as the company seeks to rebuild revenue lost in the site’s advertiser exodus. Many of the company’s top advertisers turned their back on the platform as a result of its new moderation policies, sparking concerns that a Musk-owned Twitter would see their ads appearing alongside controversial, divisive, or harmful content.  

In Thursday’s interview, Williams said moderating content on a platform like Twitter is like “hosting a party,” with people posting inappropriate content “ruining the vibe.”

While he said there was a chance Musk could still turn Twitter into a “good party,” the platform’s brand may be irreversibly damaged.

“I think brand recovery is much harder, and now the brand is very linked to Elon,” Williams said.

Advertisers weren’t alone in fleeing Twitter post–Musk’s acquisition, with users of the social network leaving the platform in droves in protest over the way the site was changing, and new competitors scooping them up.

Williams predicted on Thursday that Twitter could be headed toward a fate similar to that of Myspace or Yahoo, both of which were immensely popular in their early years but saw their brand power dwindle as poor leadership prompted users to turn to other, more relevant, platforms.

He said Twitter’s tumultuous seven months under Musk had made him question whether he and his cofounders—Jack Dorsey, Biz Stone, and Noah Glass—had made the right call in creating the platform altogether.

“Maybe we just had the wrong idea with Twitter, and now it’s time to move on to some other idea,” he said. “The idea of ‘social media’ is probably the thing I’m questioning the most right now.”

Dorsey criticism

Dorsey himself has also criticized the way Musk has steered Twitter since buying the company in late October—despite being an early supporter of the Tesla founder running the firm.

Last month, Dorsey argued that Twitter had “gone south” since Musk took over, adding that Musk should have “walked away” from the acquisition.

A year earlier, he’d said that “Elon is the singular solution I trust” when it came to finding a buyer for Twitter.

“This is the right path,” Dorsey noted at the time of accepting Musk’s proposed acquisition. “I believe it with all my heart.”

On Thursday, Williams said he was “not mad at Jack,” but said he believed his former business partner “made a mistake” in trusting Musk.

“I’m guessing it’s not going the way he was hoping,” Williams said.

Twitter did not respond to Fortune’s request for comment on the Bloomberg interview with Williams.