Mixed martial arts fighter "Unstoppable" Angela Lee announced her retirement from the sport and vacated her One Championship 115-pound title Saturday at the age of 27.

Lee, who was the ONE atomweight champion, announced her decision in an emotional speech at the ONE Fight Night 14 event in Singapore.

She has not fought since the death of her 18-year-old sister Victoria, a rising MMA star who also fought for ONE, in December.

Lee, who is of Singaporean and Korean descent and fought under the Singapore and US flags, became the world's youngest MMA champion when she won the ONE women's 115-pound title in 2016 at the age of 19.

She retires with an 11-3 record.

"I'm here today to officially announce my retirement. It has been an incredible eight years," Lee said onstage after placing her championship belt in the middle of the cage.

"I just want to say thank you to the fans, to ONE Championship, to Chatri (Sityodtong), to my teams, and to just everyone. There have been so many battles in and out of the cage," she said.

She launched a non-profit charity Fightstory to support those struggling with mental health earlier this year.

She explained backstage after the announcement that "too many things have changed" after losing Victoria, her main training partner, and that she was planning to focus her energy on Fightstory, according to Singapore's Straits Times newspaper.

Lee recently spoke out about her own mental health issues, revealing that her 2017 car crash in Hawaii was a suicide attempt and not an accident.