The couple performed the duet on NBC's The Voice earlier this month (May16) and again at the 2016 Billboard Music Awards on Sunday night (22May16).
Of the track, Blake shares that he initially only wrote the tune as means of wooing the blonde beauty.
"I only started the song to impress her," he said during an interview on The Ellen DeGeneres Show on Monday (23May16). "To be like, 'Hey, I’m writing a song about you.'" But his plan backfired slightly when Gwen, 46, contributed her own verses to the tune.
"I sent it to her, and she wrote the other half of the song," he said with a laugh. "It’s like, 'Oh, she just one-upped me.'"
The 39-year-old country star first met Gwen in 2014, when she initially joined him on the panel of judges on The Voice.
At the time, they were both married to fellow singers Miranda Lambert and Gavin Rossdale, but when their unions broke down last summer (15), Blake and Gwen turned to one another for support, and their friendship soon evolved into romance.
They went public with the relationship in November (15), when Gwen joined her man at a CMA Awards afterparty in Nashville, Tennessee, and they have been flaunting their love for one another on social media and in their songs ever since.
Of their Billboard Music Awards performance, Blake shared that it was a little odd to be singing a break-up song to his new girlfriend and they shared some laughs while on stage.
"We kinda did laugh a few times. There were moments where it was like, we're singing this song like we're going to break up. And we're not breaking up right now, it seems kinda weird," he smiled.
Blake added that he knew he was onto something special with the song, but claims he never anticipated its overnight success.
"When we wrote the song we never saw it going there," he told Ellen. "I don’t know that we ever really saw it going anywhere."