Carrie Underwood, Mike Fisher

Carrie Underwood secretly filmed her hubby, Mike Fisher, while he was singing a Garth Brooks song in the car -- and posted it on Instagram.

She used the hashtag #IAlwaysWantedToMarryGarth, with the caption, "Duet coming soon." He's no Garth, but Mike is actually a pretty good singer. 

#IAlwaysWantedToMarryGarth @mfisher1212 duet coming soon...

A video posted by Carrie Underwood (@carrieunderwood) on

Photo: Getty Images