The couple - who have been together for four years - previously released 'Go Ahead and Break My Heart' in 2016 and now they have collaborated again on 'Nobody But You', which will appear on the country crooner's upcoming new album, 'Fully Loaded: God's Country'.
Blake admitted the track was originally written just for him but he made a last-minute decision to ask his girlfriend to join him in the recording studio.
He said in a statement: "This was one of those songs where the more I heard it, the more I fell in love with it.
"I also realised how important it is for me and where I am in my life, and I think that's why [writer] Shane [McAnally] was trying to get it to me
"It fits my story. I was about to go in and record when I decided that it needed Gwen on it -- because it is our song. I think it's magic."
And the 'Hell Right' singer believes the song - which was written by Shane McAnally, Ross Copperman, Josh Osborne and Tommy Lee James - is one of the most "honest" tracks about life being made better by a loving relationship he's ever heard.
He told Nashville Lifestyles magazine: "The lyrics of that song are so on point, not just for me and Gwen, but I think for a lot of people.
"The song is not a fairytale, but at the same time it's the most epic, earth-rattling love song I've heard in a long time, because the lyrics are so honest and just say it how it is.
"This song really cuts to the honesty of how these two feel about each other, and in a real-life situation. It's as honest as you can be in a country song, and something that will make you stop your car."