can happen as well as cannot happen. If so happen the fren ur close with and you developed feel for her, then its natural cause something about her/him attracts you to developed that kind of feeling.

That feeling might not developed also and the relationship will always remain as best friend.

To develop feelings does not entirely depend on being best fren or not. The feeling just happens and its not up to us to control. The chances are higher if your best fren is of the opposite sex.