Cal. Probate Code § 6451

(a) An adoption severs the relationship of parent and child between an adopted person and a natural parent of the adopted person unless both of the following requirements are satisfied: (1) The natural parent and the adopted person lived together at any time as parent and child, or the natural parent was married to or cohabiting with the other natural parent at the time the person was conceived and died before the person’s birth. (2) The adoption was by the spouse of either of the natural parents or after the death of either of the natural parents. (b) Neither a natural parent nor a relative of a natural parent, except for a wholeblood brother or sister of the adopted person or the issue of that brother or sister, inherits from or through the adopted person on the basis of a parent and child relationship between the adopted person and the natural parent that satisfies the requirements of paragraphs (1) and (2) of subdivision (a), unless the adoption is by the spouse or surviving spouse of that parent. (c) For the purpose of this section, a prior adoptive parent and child relationship is treated as a natural parent and child relationship.