Elon Musk appeared alongside President Donald Trump at the White House Friday with a black eye, and his explanation is something most dads can relate to.

Musk was at the White House to mark his official departure as a special government employee, but he and Trump both said Musk will continue to serve as an adviser to the president.

Why does Elon Musk have a black eye?

What we know:

Asked about the black eye, Musk said it happened while he was playing around with his son, X Æ A-Xii, who he calls X . He also had an eye injury in the video Thursday announcing SpaceX’s "tentative" game plan to bring humans to Mars.

What they're saying:

"I was just horsing around with little X and I said, go ahead, punch me in the face, and he did," Musk said. "And turns out even a 5-year-old pun

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