By Nancy Kruh
May 26, 2017 01:20 PM
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Credit: Nancy Kruh

Lauren Alaina didn’t know quite what to expect from her first No. 1 party, but she sure didn’t expect this: a surprise appearance by her “Road Less Traveled” co-writer (and Grammy-winning pop star) Meghan Trainor.

Now based in Los Angeles, Trainor made the special trip to the Nashville celebration to honor not only her friend but also the inspirational hit, which the two co-wrote when Trainor was an 18-year-old unknown, starstruck by the 2011 American Idol runner-up. (“I voted for her!” Trainor, now 23, revealed to PEOPLE.)

Alaina’s jaw dropped when she spotted Trainor trying to sneak into the club where the party was held – and then the tears started to flow. The tears kept coming later on stage as the two joined co-writer Jesse Frasure, all dressed in party-themed onesies, to accept their plaques.

“Best surprise I’ve ever accomplished. I love you so much Lauren, I am so beyond proud of your first NUMBER 1 #roadlesstraveled you are my super star and my good friend and I was honored to stand next to you on stage today in our onesies,” Trainor captioned an Instagram video of the moment. “You worked your butt off and deserve all of this and more.”

In her remarks, Trainor finally confessed to sneaking a snapshot of Alaina during that long-ago songwriting session and texting it to her mother. “I was so starstruck and freaking out and I was a little creepy and I’m sorry, and the truth is out,” Trainor said.

Taking the microphone, Alaina, 22, laughingly dubbed Trainor “my creepy stalker.”

“People are always asking, ‘How the heck did you get to write a song with the Meghan Trainor?” Alaina said. “And I’m, like, ‘Thank you, first of all.’” (How could it be lost on Alaina that her friend’s career eclipsed hers as she was struggling to write and record new music?)

“She’s my friend,” Alaina declared with emotion, then addressed Trainor: “It’s been an honor to watch you bloom, and I knew the first time I met you … I was as obsessed with you as you apparently were with me. … It’s been crazy because you’re Meghan Trainor, and you’re just Meghan to me.”

Alaina, Trainor, and Frasure came together to write “Road Less Traveled” in 2012, a time when Alaina had been struggling with an eating disorder and Trainor was dealing with her own body issues.

“I’m sure we talked about it but we didn’t sit there and cry about it,” Alaina recalled before the No. 1 party. “I had some people in my life who weren’t super-encouraging, and I wanted to write a song to tell them I didn’t care about that. … It’s a serious topic but we wrote it in a super-fun way … Meghan is super-passionate about that topic, as well, so it’s just a really good fit.”

Trainor had similar recollections. “It was that time when I was writing ‘All About That Bass’ and starting to talk about my insecurities, and that’s what I bonded with Lauren about,” she told PEOPLE. “She was like, it’s so tough being in the spotlight and having your picture taken. She went through it before me and I was like, I can’t imagine what you go through – and then I had to do it.”

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Both Alaina and Trainor said they immediately knew the song was special, and the two teenagers celebrated with a silly dance around the room. “Poor Jesse,” Trainor said. “He just sat there and was like … yikes. But we loved the song so much and were so proud of it.”

Credit: Nancy Kruh

Basking in her first No. 1, Alaina is now working to push her latest single, “Doin’ Fine,” up the charts. It’s another self-written song with soul-baring lyrics, this time about her father’s alcoholism and her parents’ divorce. Both her mom and dad, she said, signed off on the song before she recorded it.

“They’ve been really good about it,” Alaina said. “Like the song says, we’re all broken. No one has a perfect family, but they’re perfect for me, and that’s what we get.”