The first reports of the American Reunion actor's engagement to the Victoria's Secret model emerged last week, but Scott initially offered no comment.
Scott confirmed the engagement rumours at American Reunion's LA premiere on Monday (March 19) when the star joked that he "doesn't know how [he] got her".
"I'm just really lucky," Scott told E! News.
The actor also quipped that he's lucky Frimodt has never seen American Reunion because otherwise he "probably wouldn't be engaged".
Frimodt has appeared in several high-profile modelling campaigns for Elle, Vogue and Calvin Klein.
American Reunion opens on April 6 in the US and May 2 in the UK.
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Watch a trailer for American Reunion below: