Cyrus, 19 and Hemsworth, 22 started dating after they met on the set of the 2009 film and the Aussie actor strengthened their relation by proposing her for marriage on May 31.
"I sort of want a finder's fee for Miley Cyrus and Liam Hemsworth. I cannot tell you. It made me cry. I remember that first day of shooting when they first kissed and Miley walked by my sister Jennifer Gibgot after they shot the kissing scene.
She goes, 'This is gonna work," Shankman said. "I'll tell you what's so great. That thing about opposites attract. Their fundamental core values are the same, but he's really mellow and she's really hyper. So it really works together. It's extraordinary, and I'm so happy. I'm scared at how beautiful those children are going to be," he added.