Extraordinary People: How can it be that DNA testing proves that Lydia Fairchild cannot be the mother of her own children? In this episode, Lydia was found to be a "chimera" where at her own conception, two separate fertilized eggs merged together instead of growing as two separate twins.
Aaron Miller, Bill Foley, Cherie Lunghi, Chris Greener, Diane Miller, Ian Watson, Kevin Carroll, Phil Taylor, Richard Lintern, Ron Taylor, Shaun Parkes, Stuart Bunce
Documentary
Maybe also available here.