A security guard at a Belgian nuclear site was shot to death two days after the Brussels terror attacks — but the slaying was unrelated to terrorism, prosecutors said Saturday.

They did not disclose the motive of the killer of Didier Prospero, who was shot dead Thursday at his home about an hour’s drive south of Brussels.

The prosecutor’s office also denied media reports that his security pass had been stolen.

Prospero was found dead in his bathroom by his three children. He had been hit by four bullets. His dog was also killed.

He was in charge of security for a nuclear research center at Fleurus.

Reports on the killing kindled fears about the possibility of militants seeking to get hold of nuclear material or attacking a nuclear site.

The fears were fueled by news reports that the suicide bombers who blew themselves up at the Brussels airport on Tuesday originally considered targeting a nuclear site, but switched their focus to the Belgian capital after the arrests of suspected militants forced them to speed up their plans.

On Friday, authorities stripped security badges from some workers at one of the country’s two nuclear plants.

Last year, investigators found a video tracking the movements of a man linked to the country’s nuclear industry during a search of an apartment as part of investigations into the Nov. 13 Paris attacks.