It's always a treat to see idol friendships play out on stage, especially when it produces powerful collaborations such as the recent performance pairing of f(x) member Amber and solo artist Ailee.

The pair sung a sizzling rendition of the 2014 hit track "Uptown Funk" by Mark Ronson featuring Bruno Mars, on the KBS music show and interview program Yoo Hee Yeol's Sketchbook.

Known to be friends off stage, Amber and Ailee complemented each other not only in their voices but also in their unique stage presence. They also drew from each other's energy and had fun on stage, which of course made for an enjoyable watch for fans of both artists.

Despite the frenetic pace of "Uptown Funk", Amber and Ailee tackled it with little difficulty as they are English-speaking natives that moved to South Korea to pursue their idol dreams.

(Fun random fact: Amber is from the West Coast of the United States, having spent her high school days in California, while Ailee grew up in the East Coast in New Jersey.)

Later in the same show, the two friends also gave performances but separately. Amber promoted her debut title track "Shake That Brass" with Ailee sang with another vocalist, reports Koreaboo.

Amber and Ailee's surprise stage collaboration is yet another proof of the numerous idol friendships the f(x) member has forged outside her agency, SM Entertainment. In "Shake That Brass", there was a parade of non-SM idol cameos, including miss A's Min, GOT7's Jackson, Rainbow's Woori, NU'EST's Aron and C-Clown's Rome, among others. She also routinely posts snapshots together with her idol-friends on social media such as guy pal Eric Nam and A Pink's Bomi.