On Thursday, news spread that Stewart – who was best known for playing Captain Jean-Luc Picard on "Star Trek: The Next Generation" and Professor Charles Xavier in the "X-Men" franchise – had died at the age of 86 following a battle with Alzheimer's disease and Lewy Body Dementia. That led to an outpouring of messages about the actor, including one from President Donald Trump's deputy chief of staff for policy.

"One of the most impactful actors in the history of film, television and theater," Miller wrote on social media.

Wheaton, who played Wesley Crusher on "Star Trek: The Next Generation" as a teenager opposite Stewart, did not care for Miller – whose politics and ideals were in direct conflict with Stewart's own – speaking out about his late co-star. And so, he fired back at the White House staffer on his Threads account.

"Stephen Miller, on behalf of Star Trek, and everyone who knew and loved him, keep my Captain's name out of your f–king Nazi mouth," he wrote. "He despised you, and everything you stand for."