(Cover) - EN Showbiz - Nicky Hilton has split from long-time boyfriend David Katzenberg, according to reports.

The American socialite and son of DreamWorks boss Jeffrey Katzenberg have gone their separate ways after enjoying a four year relationship.

Sources have revealed to The New York Post that the split was amicable between the pair, and was a result of work commitments keeping them apart.

"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," a source told the US publication.

"Nicky has been back and forth travelling overseas a lot with her business. She has recently been in Asia promoting her jewellery line, and David is starting a new production company. Their schedules never seemed to match."

The source added that the twosome hope to remain in contact, after striking up a friendship when they were in their teens. According to the pal, Nicky and David remained faithful throughout their relationship, and continue to respect each other following their break-up.

"There is no scandal or any third person -- they remain close friends, they have been friends since they were teenagers," the source added.

Nicky and David "talk regularly and have been tweeting one another".

Nicky's relationship break-down comes after the 27-year-old star's sister Paris confirmed her split from Cy Waits recently.

Representatives for the stars declined to comment. (C) Cover Media