A mutual pal of the pair tells Us Weekly that Timberlake, 28, has told friends, "it's over," and that he ended it for good — over the phone.

"It was about a month ago," the pal says.

While he was in NYC in September to show his William Rast clothing line at Fashion Week, "Justin was clearly on the hunt," the pal tells Us Weekly. At a club September 9, he dirty-danced with a tall blonde in a short black dress. At one point, she turned to her friend and mouthed, 'Oh, my God!'

Meanwhile, Biel, 27, is in "severe denial and won't accept" the split, their mutual pal tells Us Weekly.

Another source says, "There's no way of knowing if it's a firm breakup, because with them it's so hot and cold."