The couple met on the set of the 2010 drama and announced their engagement in June and Greg Kinnear - who played Miley's father in the movie - is delighted about their marriage plans.
He told E! News: ''They worked together very well on that movie, but I didn't realise how well when were doing it. It's great for them. They seem very happy.''
He also joked about giving them a week in the Georgian city where they shot the movie as a wedding present.
Greg said: ''I'll give them a week on Tybee Island. They can go back to the place where it all started.
''The truth is you can get a hotel there at a very reasonable cost. So I keep my expenditures down and I'm extending a nice gift as well.''
Miley recently signed on for a recurring guest role on TV comedy 'Two And A Half Men' while Liam started shooting the second movie in the 'Hunger Games' franchise on Monday (10.09.12), reprising his role as Gale Hawthorne.