Japanese MMA star Norifumi "Kid" Yamamoto, one of the sport's most popular fighters in the mid-2000s, died Tuesday at age 41, Krazybee, Yamamoto's Tokyo gym, announced.

Yamamoto revealed in an Instagram post in August that he had been diagnosed with cancer.

A 5-foot-4 southpaw, Yamamoto made his name as a dynamic lightweight on the Shooto and K-1 circuits. At a K-1: Hero's 5 event in 2006, Yamamoto broke the MMA record for the fastest knockout when he defeated Kazuyuki Miyata in four seconds.

Yamamoto retired with a 17-1 record following his victory over Rani Yahya on Dec. 31, 2007. The fighter would return to the ring several times, however, including for his long-awaited UFC debut at UFC 126 in 2011, when he lost to Demetrious Johnson.

After the loss to Johnson, Yamamoto had three more fights in the UFC -- all ending in defeat -- the last of which was against Roman Salazar in February 2015.