f(x) Amber Tweets Krystal a Birthday Message!

Fans trended #HappyKrystalDay on twitter and sent heartfelt messages to the group's youngest member.

In the midst of birthday messages, f(x) rapper Amber (@llama_ajol) decided to join in and tweeted, "Happy bday to our princess #HappyKrystalDay pic.twitter.com/ykIYqNUx"

The picture depicted a woman holding a llama with Krystal and Amber's faces cropped in. The word "Kryber" is an affectionate fan-made term that refers to Amber and Krystal as a pair.

Amber, who has been known to use the term before, shows just how much she really adores Krystal by also calling her a "princess."