Twitter CEO Dick Costolo has announced he’s stepping down from his role at the social media site, effective from July 1. He’ll be replaced by Twitter co-founder and current Square CEO Jack Dorsey, who’ll steady the ship as interim CEO until a permanent replacement can be found.

Costolo has been under pressure for some time, but while he’s handing over the reins he’ll still retain a seat on the company’s board of directors, according to multiple filings submitted with the Securities and Exchange Commission on Thursday. Following the disclosure, Costolo and Dorsey held a joint press conference to explain the situation, with the latter insisting that Costolo’s decision had nothing to do with Twitter’s financial performance.

“One thing I do want to make clear is that this transition is not the result of anything more than Dick deciding to move on from his role as CEO,” Dorsey said. “There is no connection with our near term results.”

Twitter’s board of directors, led by former Netscape CFO Peter Currie, will lead the search for Costolo’s replacement. Company co-founder Evan Williams and venture capitalist Peter Fenton are other notable figures on the committee, which says both internal and external candidates will be considered for the role.

Twitter’s money woes

Despite the insistence that Costolo’s exit is nothing to do with Twitter’s financial performance, investors have become increasingly frustated in over the last year, with some even calling for his head. Twitter has failed to post a single quarterly profit since its 2013 initial public offering (IPO), and in recent months things have been getting worse, with growth slowing noticeably over the past few quarters.

But Costolo insisted that this had nothing to do with his decision. It was just the right time to go, he claimed, adding that: “The scrutiny of the company would intensify if I remained CEO while the search process takes place.”

Costolo is probably right about the scrutiny. He’s been a target of angry investors for some time, and he doesn’t seem to be able to do anything to improve Twitter’s fortunes. As Fortune’s Erin Griffith noted earlier this year, Costolo has attempted to increase usage and lure old users back with a range of product improvements, but the results have been mixed. So far it seems, Twitter has been unable to translate its enormous popularity into a healthy business.

Twitter’s failings were illustrated in its most recent quarterly results. First quarter revenues topped $436 million, a 74 percent increase over the previous year, but that was still some way short of guidance. Overall, the company lost $162 million in the quarter.

But Dorsey came out in defense of Costolo in the press conference, saying: “This transition is not the result of anything more than Dick deciding to move on as CEO, and there’s no connection with our financial results.”

As for Dorsey, he now finds himself in the unusual position of leading two companies at the same time, but he said both companies have strong enough leadership teams that it won’t be a problem to combine the two roles.

In any case, Twitter’s investors don’t seem too perturbed. In fact, they seem to be positively delighted that Costolo is on his way out the door – the company’s shares rose by seven percent on the news, eventually settling up around four percent.

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