The Tonight Show host, 47, playfully confronted the 45-year-old country star about not being invited to his July wedding to Gwen Stefani on the late-night show Thursday.
Fallon showed a photo of Shelton and Stefani kissing by their cake on the big day, and The Voice coach (who appeared virtually) joked that he and his now-wife "like to take our publicity stunts all the way. So we thought we would just go ahead and seal the deal."
Bursting into laughter, Fallon said "I just thought it was beautiful. I mean, I didn't hear from you or anything, you know personally and say, 'Hey, Jimmy, what are you doing? Are you busy this week?' "
"You know what not much planning went into it. I understand. Who puts planning into a wedding, you know?" he deadpanned. "Anyway, I just remember not being invited."
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"We only had room for one NBC host at the wedding, so we had Carson," the newlywed said.
Nodding, Fallon countered, "That's true, yeah, but I've known you and Gwen for a long time and I just figured... I was just sitting at home, trying to read on Twitter, how is wedding going... anyways, it seemed like a blast!"
Hopeful that he could at least score a souvenir, Fallon asked if the couple saved him "a piece of cake." Smiling, the Body Language singer stayed silent, as the audience laughed.
Clapping back, Shelton joked that The Tonight Show host was trying to make him look bad on national television, and Fallon agreed that he couldn't be mad. Taking out another photo, he shared side-by-side throwback photos of Shelton and Stefani as kids, striking the same pose with their hands raised to their chins.
The Tonight Show Starring Jimmy Fallon
"How could you be mad at this little guy?" Fallon asked.
Without skipping a beat, Shelton said "That's back when Gwen and I used to be brother and sister," and the host erupted in hysterics.
"Way back in the day. That was years ago," he joked.
Last month, a source told PEOPLE that Shelton and Stefani couple are still basking in their honeymoon phase — and have mastered the art of balancing their busy schedules with quality time.
"Gwen and Blake are doing well. They act like newlyweds," the source says. "They have the best chemistry."