January Jones and Noah Miller attend the "Sweetwater" Premiere during the 2013 Sundance Film Festival at Eccles Center Theatre on January 24, 2013 in Park City, Utah. Credit: George Pimentel/Getty Images

It's going to be cold winter for January Jones: the actress is single again after quietly splitting with screenwriter and director Noah Miller, multiple sources tell Us Weekly. The two met on the set of the film Sweetwater, which began production in New Mexico in July 2012.

Jones was first linked to Noah in August when the two were photographed holding hands in Santa Monica, Calif. According to insiders, the two split awhile ago but kept their breakup under wraps.

The 35-year-old actress -- whose exes include Jason Sudeikis and Ashton Kutcher -- recently reunited with Noah and his twin brother, director Logan Miller, during the Sundance Film Film Festival in Park City, Utah. "They were completely fine in each other's company, so it didn't seem like it was an ugly breakup at all," a source says of the exes.

In the film, Jones plays a 19th-century widow who helps the local sheriff  take down the man who killed her husband. "They're very passionate people, very high energy," the actress said of working with the Miller twins. "When I sat down with them for the first time I wanted certain things explained, and they just won me over and got me really excited. I felt immediately that I would be in an atmosphere that I could trust them and be safe."

Noah added that he became "very close" to Jones on set and praised her stunt work in the intense film. "She shoots a ton of people in this movie, and I'm telling you, not one time did she miss," he said. "It was wonderful to see her very confident."

Mad Men's Jones is mom to son Xander, 16 months. She has yet to reveal her son's father's identity publicly.