It’s a good bet that the few of us who still follow The X-Files these days aren’t making any social plans for Sunday nights in May. (Not that the dance card of your typical X-Files devotee is exactly overbooked anyway.) That’s when Fox’s long-running sci-fi series ends its run and series creator Chris Carter promises to tie up the show’s many conspiratorial loose ends. Carter will try to ratchet up the mystery and the tension surrounding FBI agents Dana Scully, Fox Mulder, John Doggett, and Monica Reyes—but no matter how nerve-wracking the final episodes may be, fans can at least take comfort in this: Scully can’t die.

I don’t just mean it would be a downer for the series to end that way, or that her character will always live on in the memories of those who know her (“We’ll always have Queequeg!”). I mean, literally, she can’t die: Scully’s immortal.

Given the dozens of plots, subplots, and sub-subplots that have been introduced over the years, it would be easy enough to lose track of this one. But Internet fan sites have been documenting the hints about Gillian Anderson’s character since the third season’s terrific episode “Clyde Bruckman’s Final Repose,” in which Scully and Mulder hook up with a man who can foresee people’s deaths. Though she seems to know better, Scully can’t help asking the psychic how she dies. His reply: “You don’t.” But before she can find out what he means, he kills himself.

The next hint came in the sixth season’s “Tithonus,” in which Scully tracks down a photographer named Alfred Fellig, who has a habit of being around at the exact moment that people die. Fellig is no murderer, though. It turns out he’s 149 years old; Death came looking for him years ago, but Fellig turned his eyes away at the last second and has been immortal ever since. In the end, both Scully and Fellig get shot, and Death comes for Scully—but Fellig persuades her to look away, and he dies instead.

(There have been other, tantalizing suggestions. Two seasons ago, for instance, Scully encountered a woman who, like her, had survived a bout with cancer and been cured miraculously—and was still sprightly at age 118.)

Give Carter credit: It takes guts to drop a hint and not pick it up for three years. That’s just the sort of thing that earned the show its rabid fan base. But maybe Scully’s immortality was just another sign that the series was doomed. After all, The X-Files thrives on putting its main characters in mortal peril week after week. Once one of them turned out to be immortal, the show didn’t have long to live.