CANNES - Actress Karen Allen lit up the screen as spunky, hard-drinking Marion Ravenwood in the original “Raiders of the Lost Ark” 27 years ago - and then pretty much disappeared. Allen was great not only in “Raiders,” but in previous turns in “Animal House” and “Starman” - so where on earth has she been? Turns out she’s been semi-retired, living the quiet life in Massachusetts. Until now, that is. Today for the first time since the original film, she returns to the Indiana Jones saga in “Kingdom of the Crystal Skull.” She now has a young adult son named Mutt, played by Shia LaBeouf.But Allen’s not saying whether or not the father is a certain whip-wielding archaeology professor. Or is it a now-deceased RAF pilot? (Our lips are sealed.)”I was thrilled they had written me into this story,” says the 56-year-old Allen, who splits her time between Manhattan and the Berkshires, where she owns a yoga studio and knitwear design shop. “And then when I read the script I was really, really happy with what they had done with Marion.”Indy’s first and truest love - still strikingly beautiful - spoke to The Post at the Cannes Film Festival, where “Crystal Skull” premiered ahead of its worldwide theatrical bow today.The belated sequel picks up the action in 1957, when Harrison Ford’s Indy arrives in Peru with Mutt to rescue his mother from a band of Russian spies led by Cate Blanchett - and to seek the lost city of El Dorado.Allen laughed when reminded of how she told The Post a couple of years ago - while the script for “Crystal Skull” was still being written and before she had been approached - that she was certain Marion had conceived a child with Indy during “Raiders of the Lost Ark,” the first film in the series.”Did I really say that?” the freckled actress said as she flashed a grin. “I guess that was just something I was wishing for at the time.”While Allen dutifully avoided spoiling Mutt’s paternity for audiences, the actress with the striking blue eyes did sort of drop a hint. She noted that in “Raiders” there was a brief shot aboard a submarine with Marion reaching for her nightgown, after presumably spending the night with Indy.”I wake up and you’re gone,” Allen says, turning to a mildly flustered Ford during a meeting with reporters at Cannes’ Carlton Hotel.”I totally missed that,” Ford replies. “But I’m delighted that Karen could rejoin us. She’s the original relationship for Indiana Jones.”Allen did not appear in “Indiana Jones and the Temple of Doom,” a prequel that featured Kate Capshaw as Indy’s love interest. Nor was she in the most recent sequel, 1989’s “Indiana Jones and the Last Crusade,” wherein Brit actress Alison Doody did the romantic honors.With all due respect to those ladies, Indy wasn’t quite Indy without his verbal duels with Marion, who was introduced in “Raiders” in a classic scene in which she drinks a man under the table in Nepal.While there have been rumors through the years of a falling-out between Allen and Steven Spielberg, the actress said that when she was first approached by the director and “Indy” creator/producer George Lucas, they made it clear she would be appearing in the first part of the trilogy.When The Post last talked to Allen, she was waiting for a call from Spielberg after it seemed the new film was finally coming together.”Honestly, I would have been happy to do a cameo appearance if that’s all they wanted,” she says now. “But in my heart of hearts, it didn’t occur to me they would have written her into the story and not have her do something wonderful.”Among other things, Marion gets to rescue Indy from quicksand - and to kiss her hero after telling him off repeatedly for abandoning her two decades earlier. “I think Harrison and I have great chemistry,” Allen says. When Marion asks Indy about the other women he’s been involved with since “Raiders,” he replies: “They all had the same problem. They all weren’t you, honey!”Allen, who hasn’t worked in a major studio film since “The Perfect Storm” eight years ago, is also remembered for her first important part. She played Peter Riegert’s long-suffering girlfriend in “Animal House” (1978). She won a Tony Award for playing Helen Keller’s teacher in a Broadway revival of “The Miracle Worker” and has appeared in many indie and TV movies.Allen is thrilled to be back as the adventurous Ms. Ravenwood. “I think Marion matured in a really interesting way,” she says. “She’s still the same spirited person at heart.”