Jenny Mollen is opening up about a different source of frustration from her nearly two-decade marriage to Jason Biggs—and she's using Prince Harry as the comparison. In a recently resurfaced interview on the What Matters with Liz podcast, which was obtained by Page Six and recorded before the couple publicly announced their separation, Mollen said she often felt overshadowed by the American Pie star's fame. Comparing herself to the Duke of Sussex's famous role as the royal family's "spare," Mollen said she struggled with always being viewed as the less-famous half of the relationship. "To be the spare and not the heir," Mollen said. "I was the American Pie spare. I relate to Harry. That drove me mad, and I always had this feeling." According to Mollen, the imbalance began early in the relationship. When she met Biggs in 2007 on the set of My Best Friend's Girl , he was already a household name thanks to the American Pie franchise.…