Singer Rihanna was seen wearing a $400k ankle watch from Jacob And Co. at the Las Vegas Grand Prix. The bespoke timepiece was adorned with over 70 carats of diamonds and set in 18K white gold. Rihanna has had a longstanding relationship with the jeweler for over a decade. She previously wore a $670,000 watch from Jacob And Co. around her neck at a Louis Vuitton fashion show. Rihanna attended the event with her boyfriend A$AP Rocky.