Sir Paul McCartney has taken his relationship with American heiress NANCY SHEVELL to the next level by inviting her on a romantic Caribbean holiday. The former Beatle, 65, booked a break to Antigua with Shevell after his $48.6 million (GBP24.3 million) divorce settlement with estranged wife Heather Mills last month (Mar08). The pair was spotted getting close on the beach of a private resort - splashing out on a $12,000 (GBP6,000)-a-night villa. The couple have enjoyed hand-in-hand walks along the coast, a sailing trip and frolics in the sea. A source tells British tabloid The Sun, "They seemed so happy and relaxed - like they had been together for years." Last November (07), MCCartney and Shevell were reportedly spotted kissing in a car. Shevell, 47, split from her lawyer husband Bruce Blakeman shortly after.