It’s been 30 years since a team of Japanese doctors performed a colostomy reversal surgery on one of a pair of Vietnamese conjoined twins who are believed to have been affected by chemicals sprayed by the U.S. military during the Vietnam War.

Nguyen Duc, 44, the younger of the twins affectionately called “Beto-chan and Doku-chan” in Japan — after their given names, Viet and Duc — came to Japan in June 1994 to explore if Mie University Hospital in the city of Tsu could perform the operation, having underwent an initial surgery in Vietnam in 1988 to be separated from his older brother.

They are believed to have been born conjoined due to exposure to Agent Orange, a herbicide used by the U.S. forces to remove enemy cover during the war. This year marks 50 years since the end of the Vietnam War.