Who can use the name first?

So since we are thinking its a boy based off the ultrasound we have started talking names. My brother, who is not married (but has a serious girlfriend) and jokes about never having kids or at least not for a long time all the time said he already claimed, years ago, the one name I really, really like for a boy... Cole. I have never heard him even talk about baby names, much less Cole. 
What do I do?