Sienna Miller has sparked rumours of infidelity to jeans label Pepe, after being photographed wearing a pair by rival designer LoFli. The 25-year-old actress and model signed an exclusive deal in November (05) to be the "face and body" of Pepe jeans, and the fashion house fear she is not living up to her part of the agreement. A source tells British newspaper The Independent, "Not only did Sienna do a racy photo-shoot on a beach in Malibu, she also agreed in writing not to wear rival products. Not surprisingly Pepe now want her to explain what's going on. A spokesman for Pepe says, "Sienna is contracted only to wear Pepe jeans, so we're sure it must be an old photograph."