Jane Seymour Recalls Vince Vaughn Feeding 91-Year-Old Actress Outrageous Lines During Improved “Wedding Crashers” Scene (Exclusive)

Two decades may have passed since Wedding Crashers became a comedy sensation, but the memories of one behind-the-scenes moment still have star Jane Seymour in stitches.

Speaking exclusively with PEOPLE as the film returns to select theaters Dec. 11 to mark its 20th anniversary, Seymour – who proved her comedy skills playing the aggressively seductive Kathleen “Kitty Cat” Cleary — recalls one particular day on set that, in her mind, remains funnier and raunchier than anything that made it to the screen.

“The one that I will never forget was the dining table scene,” Seymour remembers, recalling the film’s memorable sequence in which the wedding-crashing leads Owen Wilson and Vince Vaughn join the Cleary family – an all-star cast including Rachel McAdams, Isla Fisher, Bradley Cooper, Christopher Walken and Seymour – for a meal.

“When you do dining room table scenes, at the best of times, they take days, and you’re just so over it by the time it gets to your coverage and there’s nothing funny about comedy when you’ve done it for four days,” Seymour explains.

However, that changed as Vaughn, who famously amped up the film’s dialogue with wild improvised lines for both himself and his castmates, spiced things up.

“We had this little old lady, and she had no idea what Vince was telling her to say,” Seymour laughs, recalling how Vaughn was feeding increasingly outrageous and risqué lines to then-91-year-old actress Ellen Albertini Dow, who played the family matriarch and was also known to moviegoers as Adam Sandler’s rapping grandmother Rosie in The Wedding Singer.

“It had nothing to do with the script, so it was, ‘Say this, say this, say this’…[and] she just went, ‘Okay’ and she kind of went with it,” Seymour says. “And we’re all sitting at the table, all really bored and tired, and now we have got belly laughs we are having to suppress because she had no idea what she was saying! And needless to say, most of what Vince put in her mouth literally was not actually in the end movie, but [some of it] did make that scene.”

“She was amazing, and she was a sport, really, because she really did not actually understand what she was saying,” Seymour adds.

Seymour says it was a treat being around such a talented cast, many of whom were experiencing high points in their Hollywood careers during the group scenes. Wilson and Vaughn had both been riding high with long winning streaks of successful films, while McAdams was hot off high-profile turns in Mean Girls and The Notebook. Both Cooper and Fisher would deliver breakout performances in Wedding Crashers that would elevate their trajectories, while Walken and Seymour were redefining their well-established images with comedic turns. 

That unique mix of performances is what ultimately elevated the movie into something special. “It had such an amazing group of actors [who] have such different ways of playing comedy that everybody was holding their own,” she says. “I always tell people that I think it’s, for me, one of the best comedy movies ever. I think it’s that iconic.”

“Vince would, as you could tell, motormouth it,” Seymour adds. “There would be a script, and then there would be Vince’s version of the script. So every day it was a question of whether Vince and Owen were on the same page, literally, with what they were going to play.”

Given Vaughn’s love for improvisation, she notes that they “kept rewriting everything all the time.”

“Except I would say that Owen honored the script,” she says. “He would add a button, but he didn’t just go motormouth over the whole thing.”

“But the fact that they were both such different kinds of comedians is what made it so brilliant,” the actress marvels. “Owen’s is very laconic…and Vince comes in like a bull in a china store, and you have no idea where he’s going to land.” 

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Yet it wasn’t just the two leads who blew Seymour away.

“Rachel McAdams was fabulous – she was very much the straight person, [while] Isla and I got all the really good laughs. We had some of the most fun on there,” Seymour recalls. “Bradley Cooper, I remember watching him and just going, ‘Oh my God, this guy’s walking away with the movie. This guy’s incredible.’ “

She was also blown away by her on-screen husband, Walken. “I’d seen him, but I was not as much of a Walken aficionado as my son Sean, who imitates him all the time, as everyone does. I had no idea what to do with his delivery…He’s genius!”

Tickets are available now for Fathom Entertainment’s release of Wedding Crashers 20th Anniversary in select theaters across the country on Dec. 11, including, for the first time ever in theatres, an additional 10 minutes of deleted scenes from the 2006 Wedding Crashers home entertainment release.