Leonardo had no idea about this fact, he was surprised, yet amazed. What would he be surprised about you may ask? Well, to be more specific, you played the (instrument of your choice), and he had no idea about it! Honestly, he was somewhat disappointed you never told him, cause this was actually so damn cool!
That day, he had been bored. So what better to do than to teleport to his best friends house and bother them?! So, he did. He teleported to your apartment/house, just to find you in your bedroom as you played your instrument. You were completely lost in your own thoughts, so you didn't even notice him staring with a surprised expression, which faded into his classic smirk as he leaned against the doorframe, watching you play.
To be honest, Leonardo felt he couldn't even say anything yet. He wanted to tease you, maybe confront you, but decided against it. At least for now. He was completely enamoured, he wanted to listen to you play a little more before he said something to you.