This is one of those only-in-Nashville song stories.

Miranda Lambert heard Meghan Trainor’s “All About That Bass” before Trainor even had a record deal.

How’d she get her hands on such a gem? As it turns out, her personal trainer is married to the sister-in-law of the guy who co-wrote it.

So, it went something like this.

1. Trainor wrote the hit pop song with Kevin Kadish in his home studio in his converted garage in Nolensville, Tennessee.

2. Then he played it for his wife Brandon Jane, one half of the country duo Coldwater Jane.

3. Then she played it for the other half of Coldwater Jane, her sister Leah Crutchfield and Leah's husband Bill, who is Lambert’s trainer. He's the man behind Nashville's Crutch Camp.

4. Crutchfield played the song for Lambert.

It’s confusing but in a good, everybody-knows-everybody-in-Nashville kind of way.

“At the end of the day, I played the song for my wife,” Kadish explained to Elle magazine recently. “And she was like, 'Girls are gonna love this.'

“Actually, this is funny: Miranda Lambert heard the song before Meghan even had a record deal because my sister-in-law is married to Miranda's personal trainer. Miranda heard the song over a year ago. And then when it came to the CMA's, she was like, 'Oh! Let's do that song.' So it's kind of full circle.”

And by the way, how did a 43-year-old man write a song that every single teenage girl (OK, every single person with a pulse) has stuck in her head?

“Maybe I'm just in touch with my feminine side,” he said, adding the songwriting session with Trainor was very organic. "We weren't acting like professional songwriters. We were just writing a song to write a song. We were just being creative and, honestly, we never thought this song would be on the radio. We never thought anyone would hear the song.”

Why are those songs -- the ones written without any commercial intentions -- usually the best ones?