Before They Were Famous: Alyson Hannigan in 'My Stepmother Is an Alien'

[caption id="attachment_121179" align="alignleft" width="300" caption="Columbia Pictures"]Alyson Hannigan in My Stepmother Is an Alien[/caption]

Though she's known these days as the sweet and innocent Lily on the CBS sitcom "How I Met Your Mother," Alyson Hannigan's biggest contribution to pop culture is indisputably her role as the sweet and not-so-innocent Michelle Flaherty in the "American Pie" franchise.

Her character's big reveal at the climax of the classic 1999 teen comedy, in which the audience's (and protagonist Jim's) perception of her goes from tame to over-the-top with one unforgettable "band camp" story, is a scene that has achieved near mythic status among millennial moviegoers, and we've all got a special place in our hearts for her because of it. However, Hannigan's very first starring role came more than a decade before she rocked Jason Biggs' world, in the sci-fi comedy "My Stepmother Is an Alien."

At the time it was a big career boost for the then 14 year-old actress, who had only appeared briefly in an independent film called "Impure Thoughts" up to that point. The movie starred Dan Aykroyd as Steven Mills, a scientist and doting father who comes into contact -- and quickly becomes smitten -- with an extraterrestrial who appears as an attractive woman named Celeste Martin (Kim Basinger). Hannigan's Jessie Mills is plenty suspicious of Celeste's strange behavior, which includes the consumption of cigarette butts and the handling of hard boiled eggs with her bare hands while they're still floating in hot water, but she's unable to convince her infatuated father that something's up until the film's revelatory conclusion.

The movie wasn't much of a hit (though it has something of a cult following among '80s babies) but gave Hannigan a career on the small screen, including stints on "Roseanne," "Touched by an Angel" and "Picket Fences." By 1997 she'd booked a regular role on The WB's "Buffy the Vampire Slayer" as Willow Rosenberg and used the show's success to land a part in the college comedy "Dead Man on Campus" before her infamous turn in "American Pie," which she'll reprise for the third time in this week's "American Reunion."

Check out the clip below for a look at the humble beginnings of the adorable Alyson Hannigan in "My Stepmother Is an Alien." It may seem strange seeing the naughty Michelle Flaherty as a well-mannered young lady on her way to prom (with a pre-pubescent Seth Green, no less!), but that's the magic of the movies.