Now more than a week after Prince’s death, fans are still wrapping themselves in the magic left behind by the legend, one who left the world too soon. They’re reading his handwritten letters, reveling in his stories, and, of course, listening to his sexy, explosive, category-transcending music.

Within his tracks, there are traces of the artist’s personal life that crack open the door to a complex figure. In Reddit’s Today I Learned community, redditor TheCheshireCody shared that Prince used the heartbeat of his unborn son as part of the percussion in a track on the Emancipation album. The child, who was named Boy Gregory Nelson, died a week after birth, having suffered from a genetic disorder called Pfeiffer syndrome.

The track is “Sex in the Summer,” and you can hear the baby’s heartbeat captured via an ultrasound at 0:14. For reference, this is what a fetal heartbeat sounds like, as posted by redditor cbbuntz.

Boy Gregory Nelson was the son Prince had with Mayte Garcia-Nelson, to whom he was married from 1996 to 2000 (and who the song “The Most Beautiful Girl In The World” is about).

Just days after the baby died of Pfeiffer syndrome in 1996, which prevents the skull from developing naturally, the couple appeared on Oprah. Unable to process their son’s death, they pretended the baby was still alive.

On hearing his baby’s heartbeat for the first time, Prince told Oprah, “I was pretty much speechless.”

“It really grounds you,” he added. “It makes you realize that things you thought were important aren’t really. That’s what it meant to me.”

Why the “Sex in the Summer” track? Here’s one redditor’s theory: