Submitted: Mar 24, 2008 - Oprah Winfrey's 13-year-old Cocker Spaniel, Sophie, has passed away of kidney failure.

"Everyone here is really sad," a source at her Harpo production company told Celebrity Dog Watcher. "Sophie was truly part of the Harpo family as well as Oprah's."

In the December issue of O, Winfrey wrote about Sophie's condition, saying that she and beau Stedman Graham were "preparing for the…