Fox News cameraman Pierre Zakrzewski died when his vehicle was hit by incoming fire in Kyiv.
He attended St Conleth's College in Ballsbridge in Dublin.
The school has tweeted it is with great sadness they have learned of the tragic passing of its past pupil from the class of 1984.
The Taoiseach says he's deeply disturbed and saddened by the killing of the Irish citizen and one of his colleagues in Ukraine.
Micheál Martin says his thoughts are with their families, friends and fellow journalists.
He condemned what he called the indiscriminate and immoral war by Russia on Ukraine.
