Brace yourselves, X-Philes: DD is going to set the record straight about the intense love affair he had last summer in LA. Taking refuge from the chilly Vancouver air in his silver Airstream trailer on the XF set, he’s not at all eager to reveal his sweetheart’s identity-he seems sort of embarrassed, maybe even a little defensive. But as the details slowly emerge, it’s clear that the actor was smitten.

The object of his desire was a stylish foreign beauty, the type that enjoys appearing topless in public. Well-built, with the kind of throaty purr that drives men mad. All in all, a real knockout.

So who was it? The truth is, well, out there. Way out. Last summer, DD’s mystery date was a brand-new red convertible. "It’s a BMW!" he confesses, almost shouting. It’s weird. When I first got it, I would lie in bed and think about my car, and I’d get a warm feeling-like it was a woman. I’d go,‘Ooh, that car. That sexy car.’

He pauses, lost in reverie.

But that’s over now, he says with a shrug, snapping back to the present. It’s just a car.

OK, so it was only an infatuation. But while the bloom may be off that particular rose, DD-dressed fro the day’s work in FBI agent Fox Mulder’s trademark dark suit-doesn’t seem to be taking it too hard. And why should he? Let’s face it: These days, the XF star can get just about any car he wants.

Nine years ago, DD walked away from a promising career in academia (he holds a master’s degree in English lit from Yale and was on his way to a doctorate when he decided to give acting a try). Today, he is one of TV’s hottest leading men.

Midway into its fourth season in pursuit of the paranormal, TXF remains a smash hit with critics and viewers alike, thriving happily in its new Sunday time slot on Fox. Member of the DDEB threaten to melt the Internet with praise for the 36-year-old actor’s marquee looks, probing intelligence, and arid sense of humor-qualities that TV Guid recently recognized when it dubbed him one of the sexiest people on TV.

There’s a suaveness about him that’s very attractive to women, observes costar GA, who plays agent Dana Scully. And the character of Mulder is cool and smart-he’s just, like, the ultimate guy.

For DD, it’s the more provocative side of his TV alter ego-the haunted obsessive who’s not aftaid to appear the lunatic in his relentless quest-that is closest to his heart. What I love about Mulder is that he’s so unconcerned with what people think about him, he explains. He’s not a nice, nice guy.

Those who know the actor well will say that there’s a hint of darkness lurking within him too. "David can be a really nice guy," Anderson declares, laughing. "He’s got the ability to be absolutely compassionate and caring. At the same time," she says, "he’s one of the moodiest people I’ve ever met. But you forgive him because he’s so charming and can be so sweet and funny."

Adds XF creator CC: He’s a person who works from self-doubt. He’s very talented, but he’s always questioning the quality of his work-which drives the level up constantly.

Relaxed, witty, and forthright as he chats in his trailer, DD at the moment appears the picture of self-confidence. Still, he acknowledges the truth in Carter’s assessment. "It’s not so much, ‘Oh, God, I’m a horrible actor’-although I do have those moments, he admits. It’s just this feeling that it’s never perfect. You want to reach that place where you’re both in and out of yourself at the same time. And I don’t get there enough.

Early in his career, it appeared DD might not have the chance to get there at all. After abandoning the ivory tower for a shot at the bright lights in 1987, he moved back to his native NY. For two long years, nothing happened. At one point, he found himself subletting a friend’s tiny apartment, an arrangement that required him to feed crickets to the friend’s pet tarantula.

"It was a sad metaphor for my existence," he says, smiling at the memory. "You’d start with five crickets early in the month, and the chirping would be this nice, hearty sound as you went to bed. As the weeks went by, the sound would get thinner and thinner, until there would be one scared little chirp. And I felt like that one guy."

It didn’t last. Following his 1989 debut in Henry Jaglom’s "New Year’s Day," DD worked steadily over the next four years in films ("The Rapture") and TV (playing a transvestite government agent in TP). He had just finished working opposite Brad Pitt in the feature "Kalifornia" when the XF pilot came along in 1993. He was sure it would flop: The subject matter didn’t appeal to him, Carter and Anderson didn’t have a track record, and Fox was hut a fledgling network. "Nothing said it was going to be any good," DD recalls.

So much for the actor’s commercial instincts. The show exploded in its third season, making DD a star. Though he reportedly earns more than $100,000 an episode, he hasn’t indulged much-new BMW aside-in the outward trappings of success. He rents a modest house near the XF set in Vancouver and typically spends the weekends reading and hanging out with his dog, Blue. "David’s a very abstemious and ascetic person who owns very little," says producer Carter. "He puts more emphasis on the work and an interior life."

Hmm, sounds like a certain FBI agent we know. "Well, Mulder doesn’t have my money," DD quips. "But I live like Mulder, even though I sleep in a bed, not a futon."

The actor and his fictional counterpart also share a certain restlessness of spirit. While Mulder tries to fill the hoel in his soul by exposing the truth about alien visitors and government conspiracies, DD’s quest for truth is a little more nebulous. "I try to balance having to live in this painful physical world and trying to open up channels to another world," says the actor, a vegetarian who practices yoga. "When you experience [the channels], you know they’re true. But when you talk about them, you’re in great danger of sounding like a knucklehead."

Of course, there’s also the search for earthly bliss. As shy, reserved kid whose older brother, Danny, used to call him ugly, the XF star is now one of HW’s most eligible bachelors. He insists that his reputation as a Romeo-some say Lothario-is overblown. "If you’re a young, single actor, you’re an easy target," says DD, who recently turned that image upside down by pretending to have a crush on his real-life pal Garry Shandling in a hilarious episode of HBO’s The Larry Sander’s Show. "But I’m single, I’ve always been single, and I’m not a monk. So take your shots."

Not that DD is afraid of commitment. He sees himself eventually getting married and having a family. What kind of woman will it take? "I don’t really have an ideal," he shrugs. "Friends who are married say, ‘Write down all the things you want and don’t want-you’d be surprised what happens.’ And I say, ‘Yeah what happens is that somebody find the list and publishes it.’"

That’s the voice of embarrassing experience talking. Last summer, DD told TVG tha he was "happy and in love"-and he wasn’t referring to his new car. Though he didn’t identify the focus of his ardor, sources confirmed that it was actress Winona Ryder-who subsequently issued a statement denying any serious romantic relationship with the XF star. DD declined to comment on the matter. But he appears to have put it behind him.

"I’ve met somebody I could settle down with," he says warily. "It’s not ideal. I think what happens is that you may have an ideal, but when you meet the person, the ideal conforms to them rather than vice versa. All of a sudden it’s like, ‘Oh, you’re ideal-I didn’t know.’"

So does that mean he’s still happy and in love? "I would never answer that now," he says, drawing the line with cheerful exasperation. "I’ll never answer a question like that again."

Strolling to the set for the next shot, DD reveals that in this ep, slated to air Jan. 5, Mulder and Scully are after a legendary Mexican creature called el chupacabras ("goatsucker"). "I think it’s an alien, she thinks it’s a fungus," he cracks. "It’s the usual thing. I’m a little bit country, she’s a little bit rock and roll."

Apparently so. Though the two stars chat and joke around as they take their marks, they seem to hardly interact at all away from the cameras. But DD says that after a period of distance, that again appreciate each other-they just need their own space.

"It’s a very complicated relationship," DD says, joking that there should be a HW therapist ("Like Dr. Katz, but real") for all the pairs of actors who play TV couples. "We just get enough of each other right now. But the bottom line is she’s the only one who knows what it’s been like for me, and I’m the only one who knows what it’s been like for her. I imagine we’ll be friends when the show’s over."

The question is, when will that be? While DD clearly appreciates all the XF has give him-money, recognition, opportunity-he’s also been very vocal about what the show has cost him: the long months spent working in Vancouver, the lack of time to pursue other roles, the frustration that comes with being identified with a fictional character. Such talk verges on heresy for some X-Philes, who resent the star’s complaints and fear that he’s going to bail out on their favorite series before its time is up.

For his part, DD finds it bewildering that people can’t understand that he just needs to blow off a little steam every now and then. "Why does everybody think that I’m this ungrateful person who is trying to leave the show?" asks the actor, who returns to feature films this spring as a drug-addicted surgeon in "Playing God." By the end of this season he points out, he’ll have given "four solid, very difficult years" to the XF. He’ ready to move on and prove himself in other areas. But he’s willing to wait.

"I have a loyalty to Chris and to the show," he says. "That’s why I’ve been here four years, and I’m gonna be here longer. I love the show. So when I talk about this ‘damn show,’ it’s like when you hear guys talk about their wives. They complain about them, but they still love them. They’re not going to leave-they just need to complain."

DD pauses for a moment. "I guess it’s my insecure way of saying that I’m more than this," he says. "Personally, professionally, in every way. Yes, this made me famous, but it didn’t give me that for free-I earned it. And people don’t get that. There’s a grain of truth there. But it’s just a grain."

In fact, contrary to what some might think, the day the series dies is not going to give DD cause for unrestrained celebration, even though it will mean his freedom.

"I’m kind of anxious about it, as much as I joke about wanting it to end," he says. "It’s going to be such a huge adjustment. I know I’m going to be sad and confused when it goes."

Of course, TXF will undoubtedly live on in the movies. In fact, DD adds, the big-screen edition of the series looks like it’s going to roll next summer. He hopes it’s the first of many. "If I bellyache about the show or the character, it’s only because it’s taking so much from me right now," he says. "I’d love to come back and do Mulder." The actor smiles. "In a girdle, or whatever he needs as he gets older."

Mulder in a girdle? Right. And DD will by then undoubtedly have a new crush on a Buick.