The seven-year-old daughter of Foreign Affairs Minister Micheal Martin has died.
It is understood Leana, the youngest daughter of Mr Martin and his wife Mary, suffered from a heart condition.
She died peacefully in Great Ormond Street Hospital, London.
Her parents and family were at her bedside.
Mr Martin and his wife said they are heartbroken at the loss of their "darling Leana".
"She was a beautiful light in our lives," they said. Mr Martin and his wife have one other daughter and two sons. They live in Ballinlough in west Cork.
It is understood Leana was admitted to Crumlin Children's Hospital on October 11 and transferred to Great Ormond Street earlier this week.
President Mary McAleese said she was deeply saddened by the news of the death.
"Leana's death is an unbearable loss for her parents Micheal and Mary, her brothers and sister and the wider Martin clan," she said.
"I know the people of Ireland will feel immense sympathy for the Martin family as they face this devastating bereavement."