Sad news for the UFO community ... Nick Pope -- known as the real-life version of "The X-Files" character Fox Mulder -- has died after battling cancer.

His wife, Elizabeth Weiss, confirmed her husband had passed in their Tucson, AZ home on Monday, posting on X ... "My heart is breaking."

She mentioned Nick had still been doing interviews in the final weeks of his life "even as he suffered," and reflected that she was "so lucky" to have been married to him, adding ... "He was a wonderful husband. I loved him dearly."

Nick announced on X in February he had been diagnosed with esophageal cancer that had spread to his liver, acknowledging at the time ... "I can't beat it."

In the lengthy announcement, he looked back on his 21-year career at the UK Ministry of Defense, where he worked, in part, as a UFO investigator.

Nick also gushed about the "true highlight" of his life ... Elizabeth. He wrote ... "She's a real-life Agent Scully: a scientist, a skeptic and a redhead."

He was 60.

RIP