<p>Carolyn Bessette cheated on new hubby JFK Jr. with "Baywatch" star Michael Bergin, the ex-flame claims in a bombshell new book. Bergin, also a top Calvin Klein underwear model, says Bessette told him she was convinced Kennedy was having his own torrid extramarital affair. The "Baywatch" hunk makes the claims in "The Other Man: A Love Story: John F. Kennedy Jr., Carolyn Bessette, & Me" - which The Post will excerpt exclusively beginning on Monday.</p>