Nicky Hilton has split from her boyfriend.

The socialite is said to have "quietly" called time on her four-year romance with David Katzenberg because their conflicting work schedules meant they were not spending much time together.

A source told the New York Post newspaper: "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.

"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."

Pals insist the split is amicable and the pair have continued to talk and communicate regularly via social networking website twitter.

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

Nicky has been getting over the split by spending time with her sister Paris Hilton - and came close to meeting a new man when she accidentally walked into a speed dating event.

She tweeted yesterday (28.07.11): "OMG. @ParisHilton and I just walked into the wrong restaurant and into a speed dating party by a mistake. Lol.

"Its a matchmaking event. Everyone had name tags. People sit + chat and then whistle blows and they go on to next mini date. (sic)"