Shankman revealed that he cried after learning of the couple's engagement, given that they met and shared their first kiss while shooting The Last Song.
"I sort of want a finder's fee for Miley Cyrus and Liam Hemsworth. I cannot tell you. It made me cry," the producer told People.
He went on to recall: "I remember that first day of shooting when they first kissed and Miley walked by my sister [producer Jennifer Gibgot] after they shot the kissing scene… She goes, 'This is gonna work'."
Shankman also explained why he believes Cyrus and Hemsworth make a wonderful couple.
"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," he explained. "So it really works together."
Hemsworth and Cyrus announced their engagement last week after three years of dating.
Cyrus's diamond engagement ring is thought to be worth in excess of $250,000 (£161,000).
Watch a trailer for The Last Song below: