The death of Geraldine Meyers-O'Keeffe, 51, at the Mercy University Hospital in Ireland was confirmed by the actor's publicist, who said the family had no further comment to make at this stage.
It is believed she succumbed to a stroke.
The tragic news sheds light on the August Rush star's erratic behavior of the past few days.
Rhys Meyers was arrested over the weekend on alcohol-related public order offenses, when he was clearly struggling to cope with his mother's ill health.
He sparked further fears of a downward spiral on Tuesday when he was spotted downing cans of super-strength cider at 11 a.m.
It is now understood that the 30-year-old--who checked into rehab for alcohol-related problems earlier this year--was turning to booze to get him through the painful ordeal of losing his mother.
Ms. Meyers-O'Keeffe--known as Gerri--lived in Glanmire, County Cork, and was hugely proud of her son's rapid rise to fame as a movie and TV award-winning actor.
She raised him single-handedly after her husband walked out on her when the Match Point star was just 3 years old, taking his two other brothers with him.
In the latest edition of Details magazine, the actor tells of how he was estranged from his father for over 20 years and found it extremely hard to accept his dad's rejection.
Rhys Meyers remains on bail following his Sunday arrest and is due to appear in Dublin District Court next month.
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