Billionaire Elon Musk bade farewell to Donald Trump in an extraordinary Oval Office appearance Friday, sporting a black eye, brushing aside drug abuse claims and vowing to stay a "friend and adviser" to the U.S. president.

As the world's richest person bowed out of his role as Trump's cost-cutter-in-chief, the Republican hailed Musk's "incredible service" and handed him a golden key to the White House.

But Trump insisted that Musk was "really not leaving" after a turbulent four months in which his Department of Government Efficiency (DOGE) cut tens of thousands of jobs, shuttered whole agencies and slashed foreign aid.