This is a proceeding to contest a will codicil. The trial court held that the codicil was a product of undue influence on testator by defendant Tibbett, a beneficiary of the codicil, and set it aside. We review de novo. ORS 19.125(3).

The burden of proving undue influence is on the contestants, Wismer and Morris. A confidential relationship between a testator and a beneficiary, when considered with other suspicious circumstances, may give rise to an inference of undue influence that, to prevail, the beneficiary must rebut. In Re Southman’s Estate, 178 Or 462, 482, 168 P2d 572 (1946). A list of potentially suspicious circumstances is set out in In re Reddaway’s Estate, 214 Or 410, 329 P2d 886 (1958).1

We find that Tibbett had a confidential relationship with testator when he executed the codicil and that suspicious circumstances surrounded the execution of the codicil.2 The trial court found Tibbett’s testimony not credible. We give substantial weight to that finding, because the judge had the opportunity to observe the witnesses. See Troyer v. Plackett, 48 Or App 497, 502, 617 P2d 305 (1980). In the light of all the circumstances, we conclude that the evidence gives rise to an inference that the codicil was a product of Tibbett’s undue influence. Because defendants did not rebut the inference, the trial court did not err.

Affirmed.