On October 19th, SM Entertainment released a mysterious 11-second teaser through their official Instagram account relating to f(x)'s upcoming comeback. 

In the video, a box is drawn with the letters V, A, L, and K at each corner, representing the names of each member - Victoria, Amber, Luna, Krystal. The text "10.21.2015 8:00 PM" then appears stating something will be released on October 21st at 8 p.m KST. From this, perhaps SM Entertainment may release a full MV or a full teaser.

However, there is more than just the release of the teaser. SM also posted a link to a special f(x) page on the SMTown website and link to a newly created Instagram account named "fx_4walls." 

On the Instagram link posted by SM, a total of 9 photos are uploaded. They form an image similar to the one in the video. One of the images says, "[4 Walls] An Exhibit". This could be the name of their upcoming album or an actual gallery exhibit.

The possibilities are endless with teasers like these!

As the anticipation continues to grow for f(x)'s comeback, this will be their first comeback since Sulli's departure earlier this year.

Watch the teaser here.