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After less than a year of dating, Miley Cyrus and Justin Gaston have called it quits, Usmagazine.com has learned.

The two split on Sunday, a source tells Us.

"They have been having trouble for a while," says the insider. "It's been hard for a long time since Miley has been working so much and traveling a lot."

Contrary to reports, Cyrus' ex Nick Jonas "was not the reason for the split, but they have been spending time together."

Added the source, "Miley and Nick are working on a couple different projects together. Justin has been a little jealous of that."

The 16-year-old Hannah Montana star -- who recently flew to Savannah, where she will be shooting the upcoming Nicholas Sparks drama, "The Last Song" -- hinted at a split over the weekend when she told Us that Gaston, 20, won't be joining her on the road.

"He's got his own thing going on," Cyrus told Us. "But I am just continuing to work hard and definitely have the whole tour going on and my clothing line and the movie."

A rep for Cyrus had no comment.

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