Billy Ray Cyrus tells ABC News he doesn't know if daughter Miley Cyrus and Liam Hemsworth will make it down the aisle because they're young and kids. Credit: Steve Mack/Getty; Charley Gallay/Getty

While penning his new memoir Hillbilly Heart, Billy Ray Cyrus didn't want to say too much about daughter Miley Cyrus' engagement to Liam Hemsworth -- just in case it didn't work out! The country star and father of the 20-year-old singer admits he's not certain that the couple will make it down the aisle.

"I know as I was writing the book I wanted to keep that particular moment as open-ended as possible," Bill Ray, 51, tells ABC News in a new interview. "I didn't know the answer. They're young. They're kids. The great news is, they're great friends. They're really, really good friends. If you end up getting married, that's your business too, you know?"

Miley and Hemsworth, 23, became engaged in June 2012 after falling in love on the set of their film The Last Song in 2009. The couple hit a rough patch in their engagement last month, but the "Can't Be Tamed" singer insisted they have not called off their wedding.

Does Miley's dad think they will make it the aisle?

"I don't know. I really don't," he said. "I play it by ear and I know whatever is meant to be, that's the way it's going to happen."

Miley -- who was briefly estranged from her dad in 2011 -- hasn't commented on her father's opinion of her relationship yet, but did tweet on April 14, "Dad and I are so in sync sometimes it's crazy. The book. Billy Ray Cyrus."