Shelby Lynne and Allison Moorer may have been the headliners of their Side-by-Side tour that stopped for two nights at the legendary Birchmere in Alexandria, Virginia, but young John Henry Earle stole the show.

During the sisters' encore at the November 29 show, Allison held 7-month old John Henry (her son with fellow musician Steve Earle) in her arms as she sang. The cooing, wide-eyed baby soaked in the audience's cheers and awwwws with wide-eyed amazement much to the sisters' apparent joy.

"I do love you like the devil," Shelby told her sister at one point in the show before she introduced her nephew to the crowd.

"I do [love you] too, you know," responded Allison.

Anyone who sees the sisters interact can tell you that the words are almost unnecessary. Although there's plenty of false sentiment during the holiday season, it's clear the sisters' affection for each other is the real deal. The bond between them has only grown through the years, even though they live on opposite coasts and both have demanding careers.

'Without a doubt we grew up listening to the Everly Brothers and Elvis Presley and pop music from the '30s and '40s era," Shelby tells The Boot. "That's where we learned harmonies."

Allison wrote a song in that style which she had planned to record with her sister, but schedule conflicts torpedoed the idea. That's a shame, as anyone who heard the emotion-filled rendition of 'Where You Are' performed at the Birchmere would likely attest.

"I wrote that song years ago for the two of us," said Allison. "When it didn't work out, I ended up singing both parts ... I'm so happy I finally get to sing it with you."

This is the sisters' first tour together but that's not because of lack of desire. Living on opposite coasts and juggling two hectic careers kept their dream to work together at bay until this year when the promotions for Allison's album 'Crows' and Shelby's album 'Tears, Lies and Alibis' wound down about the same time.

"We are not going to take a band on this one," Shelby told The Boot prior to the concert tour. "It will just be us and our guitars. If we do more, we might entertain taking some players with us, but now it's us, two guitars and maybe if I can get a piano at a venue I might play that a bit, but we want to keep it simple."

Not to mention beautiful. The sisters worked their way through a handful of holiday songs including some from Shelby's just-released album 'Merry Christmas,' as the air sparkled with electricity, their lush harmonies filling the venue as the two melded their vocals on 'Silent Night' and other favorites.

"One of the earliest memories I have is singing Christmas songs with Sissy," said Allison using the term of endearment by which she and Shelby refer to each other. "I don't even remember a world without Sissy in it, and I don't remember a world without music."

Each song holds a special memory for the sisters.

"I always remember singing 'Winter Wonderland,' said Allison of family singalongs. "I really loved singing it. It's great to do these shows around the holidays because we love to sing these songs and audiences love to hear them."

At the conclusion of the 90-plus-minute concert, during which the sisters announced early plans to record an album together next year, Allison and Shelby gathered backstage with a handful of close friends and family including Allison's husband and their son.

As Allison, Shelby and Steve took turns holding John Henry, the baby remained the center of attention, staring at bright colors, gurgling and gazing at those who were lovingly admiring him. It was just that kind of night.

"Singing together, it's the old familiar uniform that feels so natural," says Shelby. "We have never done anything else as well as sing together. Sometimes I have to pinch myself and say 'Are we really doing this?'"

Shelby and Allison continue on tour together. Check here for upcoming dates.

More From TheBoot