How to tell your best friend that you had made another best friend without hurting her feelings?

-I have found a super cool best friend but i dont know how to to tell my old best friend about it you might be wondering why i would leave my old best friend that has some personal reasons I wanna tell her that i have found another best friend but i dont know how to do that. Thanks =)dont. just hang out with her less and less and soon you will loose contact. easy&simple (:you can have two best friends. but you dont really have to tell her just if she asks whos your best friend just say i dont know prob (put the other girls name here) and if she looks sad just say no maybe you idk i have alot of best friends