Deciding an issue left open in Barefoot v. Jennings (2020) 8 Cal.5th 822, this decision holds that heirs who would take by intestate succession have standing to sue in probate court to invalidate a trust disposing of the decedent’s estate to a third party on the ground of undue influence, lack of capacity, and forgery. Probate Code 17200 states that trustees and beneficiaries may petition to invalidate a trust, but it does not say that others may not do so as well. And the intestate heirs here clearly had an interest in invalidating the trust since if they succeeded in doing so the estate property would flow to them rather than the third party with whom the decedent had lived during her last few years of life and whom the trust named as trustee and sole beneficiary.