Publicist Lizzie Grubman has split with her husband, Chris Stern, after nearly five years of marriage. The couple, who have two children, Harry, 4, and Jack, 2 next month, are living separately and telling friends they have grown apart because of their busy work and travel schedules. Her company, Lizzie Grubman PR, handles publicity and management for stars including Shanna Moakler and Billy Baldwin, while Stern is a partner at marketing and branding company Safari Sundays. Grubman, daughter of entertainment lawyer Allen Grubman, insists the split is amicable and there’s nobody else involved. She told us, “We can confirm that we are separated. We remain the best of friends and our main concern is the well-being of our sons.” Lizzie and Chris began dating in 2005 and married in March 2006 with a reception at Cipriani 42nd Street packed with boldface names. No divorce papers have yet been filed.