Kristen Stewart may not be a mom herself, but she definitely related to Princess Diana's maternal side when she portrayed her in the film. «The whole thing about watching her, within that space when her children are close to her, it's a nucleus. It's a three-headed animal, sort of an unstoppable beast,» Stewart told ET's Lauren Zima of the late Princess of Wales' relationship with sons Prince William and Prince Harry. "...You don't want to mess with moms, you just don't do that.