Elon Musk cheated Twitter shareholders by waiting too long to disclose his growing stake in the company, the U.S. Securities and Exchange Commission claims.

Twitter's stock price rose 27 percent once Musk belatedly disclosed his stake, the lawsuit said. "During the period that Musk was required to publicly disclose his beneficial ownership but had failed to do so, he spent more than $500 million purchasing additional shares of Twitter common stock," it said.