The `Avatar` actor dated fashion stylist Natalie Marks for almost three years after meeting her at the offices of Shanahan Management, which represents Sam and was where Natalie used to work, but the pair have not been spotted together since last October when they attended a basketball match at New York`s Madison Square Garden.
A friend of the former couple revealed the split was no surprise to those close to them, telling Australia`s Daily Telegraph newspaper: "It has been on the cards a while, I believe."
Pals of Sam believe his splitfrom 24-year-old Natalie could be responsible for his uncharacteristic outburst at the G-day LA event in Los Angeles on 22.01.11 when he slammed his fist in to a wall after being asked to wait before walking the red carpet.
The 36-year-old actor also left his seat at the gala a number of times and was reportedly overheard swearing.
However, his mood appeared to have lightened by the end of the event as he made a generous bid at the charity auction, raising his initial offer from $20,000 to $50,000 for a four-night stay at a luxurious resort on Hamilton Island, which is located at the Great Barrier Reef in Australia.
Sam then reportedly hosted a bash in his hotel room at the Chateau Marmont which went on until the early hours of the morning.