New Zealander Rob Hamill is to testify next month at the Cambodian war crimes trial of the Khmer Rouge commander of the camp where his brother was killed.
Mr Hamill is to appear at an Extraordinary Court of Cambodia trial of the commander known as "Comrade Duch", almost 31 years to the day after Kerry Hamill and Englishman John Dewhirst were kidnapped from their yacht.
A fellow sailor, Stuart Glass of Canada, was killed.
Hamill and Dewhirst were tortured for two months at Camp S21, then executed after being forced to admit they were CIA spies.
Mr Hamill says he expects to experience the widest possible range of emotions when he sees Duch.