Nathan's first Crush

We were at Walmart yesterday, and this little girl from Nathans preschool class, came up to him and said "Hello, Nathan". He runs away and hides in a different isle. When I get to him, he crying. I try to come calm him down, and make him go say hi back. This little girl has been in his class for two years now, and they only have a total of 8 kids in his class. So I didn't understand why he was so scared. I thought maybe she had been mean to him, since I know he's so sensitive. But he hid behind me and refused to say Hi. Later that night I finally found out why. J.R. comes home, and I told him the story, he goes up to Nathan and ask him if he thought she was cute and Nathan starts crying and says, "She's so Beautiful!".
I can't believe my four year old, is already shy over a girl.