The Minority Report star made an unannounced stop at the Our Lady's Children's Hospital in Dublin to spread some festive cheer.
Farrell, who has two young sons, spent four hours chatting with sick kids, including two-year-old Max Wenman, who was diagnosed with cancer in July (12).
Max's godfather Eddie Brennan tells the Irish Sun, ""We'd a rough idea Colin might stop in because he tends to visit on Christmas Day, but it was more of a hope than anything. He came in and met Max and his dad Roy, he stayed for at least 10 minutes, chatting about anything and everything, and he couldn't have been a bigger hero. The kids were delighted to see him but I think the nurses were even more excited! He's a total legend.""
Farrell is a regular visitor to the hospital, and also spent Christmas Day there last year (11).