Nicky Hilton and her producer boyfriend David Katzenberg have broken up after dating for about four years, sources told the New York Post.

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Hilton is the sister of model-actress Paris Hilton and Katzenberg is the son of DreamWorks co-founder Jeffrey Katzenberg.

"They broke up quietly after four years together. The main reason was that they have been busy with their work schedules, and it has made it difficult to spend time together," one insider told the Post.

"Nicky has been back and forth traveling overseas a lot with her business. She has recently been in Asia promoting her jewelry line, and David is starting a new production company. Their schedules never seemed to match. ... There is no scandal or any third person -- they remain close friends, they have been friends since they were teenagers."