A legendary Korean hip-hop group reunited to celebrate their twentieth anniversary.

Turbo, made up of "Running Man" star Kim Jong Kook, Mikey, and Kim Jung Nam, came back on Dec. 21 with their song "Again." Fifteen years since their last release, the group returned with a chart topping album on Monday. 

The group's comeback album "Again" contains 19 songs, and features multiple guest artists.

"Again" topped multiple Korean music charts following its release on Dec. 21. 

The album's title track, "Again," is an upbeat dance song that features Korean TV personality Yoo Jae Suk, who is also one of Kim Jong Kook's "Running Man" co-stars.

The album also featured artists like Lena Park, Lee Ha Neul, Jinu, Lee Sang Min, San E, and Soya. Soon Il Sang also produced a song for the album.

Turbo debuted in 1995 as a duo featuring Kim Jung Kook and Kim Jung Nam.

The group saw major success with songs like "My Childhood Dream," but in 1996 Kim Jung Nam decided to depart from the group. In 1997, Kim Jung Kook joined with Mikey to release a third album, "Born Again." As a duo, Mikey and Kim Jung Kook released two more albums before going on hiatus in 2000.

"Again" is the first album the three Turbo members have released together, and is a follow-up to their performance at last year's "Infinite Challenge" special event, TOTOGA. TOTOGA featured first generation K-pop singers, and reignited interest in groups like Turbo and S.E.S.

The music video for "Again" was released on Dec. 21 and featured Turbo's members as well as "Running Man" stars Lee Kwang Soo and actor Cha Tae Hyun. The song was released in both Korean and Chinese, and topped Melon, Mnet, Bugs, and other Korean music chars immediately following its release. 

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