Mark Cuban, the outspoken billionaire who publicly offered to be the potential running mate to both Hillary Clinton and Donald Trump, could not keep himself from attacking Trump during the DNC Convention on Tuesday.

Cuban, who owns the Dallas Mavericks basketball team, went to Twitter and suggested that Donald Trump hasn’t released his tax returns because he doesn’t want the world to see that Hillary and Bill Clinton earn more money than he does.

The media-hungry billionaire questioned if the Clintons paid more in taxes than Trump has made in income. According to her tax returns, the Clintons paid more than $43 million in federal taxes on $141.9 million of income earned between 2007 and 2014.