What is the burden of proving undue influence on a will?

The burden of proof of undue influence is on the attackers of the will to prove that the mind of the testator was over borne by the influence exerted by another person such that there was no voluntary approval of the contents of the will. Suspicious circumstances may rebut the presumption of testamentary capacity and knowledge and approval of contents, so as to place the onus on those who advance the will, but the burden of proving undue influence or fraud remains on those who allege it. (The leading case is Vout v. Hay, 1995 CanLII 105 (SCC), [1995] 2 S.C.R. 876.)