P Diddy has reportedly been dumped by his longtime girlfriend - also the mother of his three children - Kim Porter, and Sienna Miller (pic) is rumoured to be the reason.

The New York Post reports that Porter called time on her relationship with the rapper amid persistent rumours that Diddy and Sienna were having an affair. The Factory Girl star and the music mogul are known to be close friends, and were most recently pictured together at the after-party following Concert For Diana last weekend (July 1).

If the split is true, it's a sad case of deja vu for Diddy - aka Sean Combs and Porter, as the couple split for several years when he cheated on her with singer and actress Jennifer Lopez. But when Lopez dumped Diddy in 1999, he went back to Porter. Seven months ago, in December 2006, Porter gave birth to twin girls D'Lila and Jessie. The couple also have a ten-year-old son together called Christian.

Sources inside Porter's camp told the New York Post that she has moved out of his apartment in New York and has no plans to return, although the split is said to be amicable. The source said: "Kim is in Louisiana filming a movie right now, and when it's done she's moving to LA. They are the best of friends, but they just can't be together right now."

So far spokespeople for Combs are denying the split.

naija girls can learn alot from kim porter