f(x)'s Amber and 4minute's HyunA are known to be pretty good friends and it looks like it's going strong. Amber posted a picture of herself with HyunA on her me2DAY saying, "Huh? Huh? Birthday? Ah~Today is 4minute HyunA sunbae's birthday! Friend! Happy birthday!" HyunA turned 18 in American age on the 6th. Let's all wish her a belated birthday! Amber added, "HyunA! Do well with promotions and I will always cheer you on! HyunA fighting! 4minute fighting!" Aren't they the cutest?