What is the burden of proving knowledge and approval of a will in relation to allegations of fraud and undue influence?

A different test applies in relation to the allegation of undue influence. That is an affirmative defence that those attacking the will must prove. The court said in Vout v. Hay at ¶28: … No doubt this reflects the policy in favour of honouring the wishes of the testator where it is established that the formalities have been complied with, and knowledge and approval as well as testamentary capacity have been established. To disallow probate by reason of circumstances merely raising a suspicion of fraud or undue influence would tend to defeat the wishes of the testator in many cases where in fact no fraud or undue influence existed, but the propounder simply failed to discharge the legal burden. Accordingly, it has been authoritatively established that suspicious circumstances, even though they may raise a suspicion concerning the presence of fraud or undue influence, do no more than rebut the presumption to which I have referred. This requires the propounder of the will to prove knowledge and approval and testamentary capacity. The burden of proof with respect to fraud and undue influence remains with those attacking the will.