f(x) start their comeback hype!

f(x) finally set the green light for the comeback as SM releases mysterious images on @fx_4walls instagram accounts and a video clip on the group's website.

But to delight every f(x) fans out there, rest assured that the girls have a surprise on October 21 at 8PM although it's not yet clear if it's their comeback date.

The instagram photos make a symbol out of boxes with members' initials V, A, L, and K along with the words [4 Walls] An Exhibit emphasizing the revamped quartet!

Anticipate every release starting today!