On the one hand, the two influential tech CEOs are close friends and business associates; on the other hand, Musk is genuinely worried that Page might just lead to the destruction of humanity as we know it.

"I'm really worried about this," Musk is quoted as saying in Elon Musk, a new authorized biography of the CEO of Tesla and SpaceX.

"This," according to the book, refers to the possibility that Page would develop artificially-intelligent robots that could turn evil and have the ability to annihilate the human race.

Page may be well-meaning, but as Musk says, "He could produce something evil by accident."

Google has acquired more than half a dozen robotics companies to date, but the company's ultimate goal for robots is unclear.