Archbishop Desmond Tutu has sent a message of hope to supporters of Omar Deghayes, the Brighton man held in Guantanamo Bay.
Speaking to The Argus during a visit to Sussex, the clergyman and human rights campaigner compared those in the US prison in Cuba to people detained in South Africa during the apartheid era.
He urged those involved in the Justice for Omar campaign, supported by The Argus, to stay strong for Mr Deghayes and his fellow prisoners.
Dr Tutu said: "Tell them injustice and oppression won't have the last word - that one day they will be vindicated.
"In South Africa I opposed detention without trial and I have no reason to change."
The Nobel Laureaute was at Lancing College to dedicate a stained glass window to a former pupil of "incredible eloquence and passion".
Bishop Trevor Huddleston, who died in 1998, was posted to South Africa at the age of 33.
He was ordered home in 1955 for opposing the Bantu Education Act - enforcing racial segregation in education.
The following year, he published Naught for your Comfort, attacking apartheid.
Father Huddleston went on to become bishop of Stepney, archbishop of the Indian Ocean and president of the Anti- Apartheid Movement.
Dr Tutu said: "If there is anyone who helped keep the issue of apartheid in the public domain, that person is Trevor Huddleston."
He said he first met Fr Huddleston when he was a boy, in Sophiatown, South Africa. The English priest doffed his hat to Dr Tutu's mother - a gesture from a white man to a black woman that was unheard of. When Dr Tutu developed TB as a young man and spent almost two years in hospital, Fr Huddleston visited him.
Fr Huddleston befriended many prominent black South Africans, including Nelson Mandela.
It was reported this week that Dr Tutu's prostate cancer had returned. But he said he would have come from "any point of the globe" to the ceremony "to honour a wonderful, wonderful man".
Lancing College headmaster Jonathan Gillespie said: "It is a huge honour Desmond Tutu has come to see us in honour of one of our most distinguished students."
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