Elon Musk is under investigation into potential breaches of insider trading rules.
The enquiry has been launched by the US Securities and Exchange Commission.
It stems from a tweet from the Tesla CEO last year, where he put up a poll asking if he should sell 10 percent of his stock in the company.
Business journalist Gavin McLoughlin says Elon Musk's brother is also facing the same probe:
"When you get the CEO weighing up whether to sell shares... That's probably going to have a negative impact on the share price, right? So, what the regulators seem to be concerned about is, the day before this poll went up on Twitter, Musk's brother, Kimbal, sold some Tesla shares."
