John F. Kennedy Jr. always regretted not introducing his wife Carolyn to his mother, Jackie Kennedy, according to Once Upon a Time: The Captivating Life of Carolyn Bessette Kennedy author Elizabeth Beller. “Jackie was quite sick [with non-Hodgkin’s lymphoma] and it wasn’t a moment to [meet] a new girlfriend,” the writer explained in a recent interview. “But he told many friends… one of his biggest regrets in his life was not introducing them, because that… hurt Carolyn.” JFK Jr. and Carolyn tied the knot in 1996, two years after his mother’s tragic passing. However, their three-year marriage…