Newly-single pop star Nick Lachey is pumping up and cashing in as the star of a new US infomercial for celebrity personal trainer GUNNAR PETERSON. The former NEWLYWEDS: NICK AND JESSICA star pocketed $500,000 (GBP294,000) for his appearance in the ad - which sees him strip off his shirt to reveal his toned physique. Peterson claims, "Nick came in looking really good and left looking great." The celebrity personal trainer whipped Lachey into shape a few months before filming the shots last summer (05) for the CORE SECRETS DVD series. Peterson, who also trains Jennifer Lopez, adds, "Nick doesn't shy away from hard work."