Equatorial Guinea is to release a South African imprisoned two years ago after being convicted of plotting to overthrow President Teodoro Obiang.
The coup attempt was uncovered when a plane was impounded
Marius Boonzaier was critically ill and was pardoned and will be released on humanitarian grounds, a South African spokesman said.
Six South Africans are among 23 suspected mercenaries in prison after being convicted over the same plot.
Alleged ringleader Simon Mann is serving four years in jail in Zimbabwe.
He was arrested there after apparently purchasing weapons for the planned coup attempt.
A Zimbabwean court sentenced more than 60 others found on a plane impounded in Harare on relatively minor charges.
Sir Mark Thatcher, son of former UK Prime Minister now Baroness Thatcher, was fined and received a suspended sentence in South Africa for his involvement in the affair.
Relatives of those being held in Equatorial Guinea complain of abuse and unfair treatment.
One suspect, a German, died in prison after what Amnesty International said was torture.