Idol star buddies and SM Entertainment labelmates Super Junior's Heechul and Girls' Generation's Taeyeon got together recently, and Heechul made sure to support Taeyeon's solo debut with "I".

The two are well-known as close friends among fans, and Heechul mentioned the nickname of the duo on Instagram on October 10. He posted the photo above of himself holding up her album as well as the message, "Bipolar siblings." 

Fans responded, "I really really like you because you always seem like a brother and protect Taeyeon," "Fighting Taeyeon," and more.

Have you heard Taeyeon's debut song yet?