Tesla Chief Executive Elon Musk's brother, Kimbal Musk, who is a Tesla board member, sold 27 million worth of Tesla stock on Thursday, according to regulatory filings. That comes as TSLA stock has retreated in recent days to a critical juncture.

Musk, who also runs SpaceX and a number of other companies, has been known to make big often exaggerated promises. For example, he once called the Hyperloop, which was never built, the "fifth mode of transport" and famously promised to take Tesla private in a Twitter post, saying he had secured financing that he didn't have.