Person A is a super cocky and witty acting person who tries not to show lots of sentiment. One night while a pregnant person B is sleeping beside them, A sits up and says B's name a few times. B is deep in sleep and A smiles. They lean really close to B's stomach.
"Hey little _____ junior. You don't know this yet, but I love you more than anything in the world, well, maybe besides B, but I love you both so much."
A proceeds to softly sing a lullaby while rubbing B's stomach. After about 10 minutes, A kisses B's stomach 
"Goodnight, (baby name) I love you." 
A turns over to go to sleep and hears B say 
"I didn't know you could sing like that" 
A is super embarrassed and can't speak. B thinks it's incredibly sweet