Cian McDonnell Lynch has lost his battle with Dyskeratosis Congenita, a rare bone marrow failure syndrome.
The four-year-old, from Carlanstown in Co. Meath, went to hospital on Thursday for an elective PEG insertion and liver biopsy.
He was brought to ICU yesterday and passed away this evening.
His family shared the heartbreaking news on the official "Hope for Cian" Facebook page.
Earlier this year, the McDonnell family were further devastated when Cian was diagnosed with microscopic pulmonary AVMS.
At this time, they were told by doctors in London’s Great Ormond Street Hospital that he had only months to live.
His parents, Lisa and Donal, and his sister Chloe
have been tirelessly campaigning for Cian and his story has touched the hearts of the nation.
Our thoughts are with his family.