Amnesty International is calling on the Egyptian authorities to immediately release Ibrahim Halawa.
He is the son of Ireland's most senior Muslim cleric and has been held in an Egyptian prison for 463 days without trial.
He was arrested following the overthrow of President Mohamed Morsi.
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His three sisters - who were arrested at the same time - were allowed to return to Ireland.
Today is Ibrahim's 19th birthday and a candlelight vigil is taking place outside the Egyptian embassy in Dublin today.
Colm O'Gorman of Amnesty International Ireland says Mr Halawa is innocent and must be released.