Billionaire Elon Musk, President Donald Trump’s right-hand man, used a disability slur against an astronaut on his social media platform X after the astronaut accused him of lying.

In a joint interview with Trump conducted by Fox News’ Sean Hannity that aired Tuesday, Musk said that astronauts Butch Wilmore and Suni Williams, whose return from the International Space Station has been delayedfor months, have been left in space for “political reasons.” 

Both astronauts have rejected the notion that they are stranded. Wilmore told CNN’s Anderson Cooper in a February 13 interview that they “don’t feel abandoned.” Williams added that they were “doing pretty darn good, actually.”

Musk’s speculation about why the astronauts are still in space struck a nerve with Andreas Mogensen, a Danish astronaut with the European Space Agency, who posted on X: “What a lie.”

“And from someone who complains about lack of honesty from the mainstream media,” Mogensen added.

Musk responded to Mogensen with vitriol: “You are fully retarded,” he posted on X.

“SpaceX could have brought them back several months ago. I OFFERED THIS DIRECTLY to the Biden administration and they refused. Return WAS pushed back for political reasons,” he added. “Idiot.”

Musk’s offensive language is in line with many of his past controversial comments and actions, including his Nazi-like salute after Trump’s inauguration. 

Yet Trump has made Musk a very visible sidekick, so much so that CNN panelists joked that Vice President JD Vance should be concerned by their relationship. Within a month of Trump’s inauguration, the two have already done a joint interview and press conference.

Trump put Musk “in charge” of the makeshift “Department of Government Efficiency,” which he tasked with cutting government costs. As a result, thousands of government employees have been fired or laid off just one month into Trump’s term.

Nearly two dozen federal workers have filed a lawsuit against Musk claiming that his actions via DOGE are unconstitutional. However, the judge in the case hasn’t blocked him or DOGE team members from moving forward with cuts or accessing privileged information.