Ever since Blake Shelton and Gwen Stefani first became an item, their relationship has left some fans scratching their heads: At first glance, the pair don't seem to have all that much in common.

Stefani comes from the pop world, and when they first met on the set of The Voice, she didn't even know who Shelton — a country superstar — was.

But this couple always had some common ground (they both went through high-profile divorces around the same time), but their connection is more evident than ever when you examine their childhood photos side by side. That's just what Shelton and the late-night television audience did during the singer's appearance on The Tonight Show Starring Jimmy Fallon on Thursday night (Dec. 2.)

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Show host Jimmy Fallon held up two photos, put next to each other, one of a young Stefani, and the other of Shelton at around the same age. The resemblance is pretty striking. They're both offering cheesy, little-kid smiles to the camera, both have their chins rested on one of their hands and both photoshoots went with a Western theme. Shelton's leaning up against a hay bale in his picture, while Stefani wears a blue cowboy hat in hers.

Even Shelton couldn't deny the similarities. "That's back when Gwen and I used to be brother and sister," he jokes. "Way back in the day. That was years ago."

Elsewhere in the interview, Shelton recounts details from his wedding to Stefani, which took place over the summer, and explains the backstory behind how he decided to write a song as his wedding vows. That song, "We Can Reach the Stars," is available on the deluxe edition of his Body Language album, which arrived this week.

Shelton and Stefani's wedding was a family-oriented affair set on Shelton's Oklahoma ranch, and not many celebrity guests were in attendance, with the notable exception of Carson Daly. Daly, who is particularly significant to the couple because he's the host of The Voice, where they met and fell in love, officiated the wedding.

But Fallon is a longstanding pal of Shelton's, too, and during their conversation, he poked some light-hearted fun at the fact that Shelton didn't invite him to the nuptials — or even save him a piece of cake!

"We only had room for one NBC host at the wedding, so we had Carson," Shelton deadpans in response.

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