Last Friday, the celebrity couple paid a visit to Universal Studios Hollywood.
But after a couple of glasses, Legend noticed that the CityWalk stage was empty and couldn't resist hoping up for his moment in the spotlight.
The singer warbled his way through his 2013 hit 'All of Me'.
And while the lyrics were originally about Chrissy, in his drunken state, John decided to change them to make the song about himself.
"John got wine drunk and sang a song at Universal Studios last night,” Chrissy wrote alongside the video.
"The whole joke was supposed to be that literally no one was watching or at the stage but then he got on stage and was like IT'S ME JOHN LEGEND," she added.
However, John has a different version of events.
"We went to Universal Studios last night to do Horror Nights before they shut it down. Costume theme was onesies,” he wrote on Instagram.
"We bought a few new ones and raided the closet too and found the perfect one for me to wear. Someone made Chrissy a onesie with my face on it and of course I had to wear it. Then I found a reluctant DJ with a mic and serenaded myself. It was a night."