Cal. Probate Code § 6453

For the purpose of determining whether a person is a “natural parent” as that term is used in this chapter: (a) A natural parent and child relationship is established where that relationship is presumed and not rebutted pursuant to the Uniform Parentage Act (Part 3 (commencing with Section 7600) of Division 12 of the Family Code). (b) A natural parent and child relationship may be established pursuant to any other provisions of the Uniform Parentage Act, except that the relationship may not be established by an action under subdivision (c) of Section 7630 of the Family Code unless any of the following conditions exist: (1) A court order was entered during the parent’s lifetime declaring parentage. (2) Parentage is established by clear and convincing evidence that the parent has openly held out the child as that parent’s own. (3) It was impossible for the parent to hold out the child as that parent’s own and parentage is established by clear and convincing evidence, which may include genetic DNA evidence acquired during the parent’s lifetime. (c) A natural parent and child relationship may be established pursuant to Section 249.5.