Biggs and Hannigan play couple Jim and Michelle, whose wedding was the central story in the third instalment of the comedic franchise.
The duo recently did an interview with Collider, where they agreed that it was "about time" that Jim's penis is revealed.
"Honestly, I think with Jason Biggs, it was about time!" Hannigan said. "We spent three movies talking about it, and the pie got to see it, so it was about time that we all get to see it."
Biggs also shared his thoughts on it: "The penis has been a major player in the American Pie franchise. It has been its own character."
American Reunion features the original cast, including Chris Klein, Mena Suvari and Tara Reid, as they meet up again for their high school reunion.
Suvari recently shared that the chemistry of the cast is still intact through the years.
"It feels like no time has passed at all," she said. "We have so much chemistry with one another that it's so natural. It's the same vibe."
American Reunion arrives on April 6 in the US and May 2 in the UK.
Watch a teaser trailer for American Reunion below: