Final answer:
The undue influence defense is applied when there is suspicion or proof of the testator being manipulated or coerced at the time of making or changing their will, possibly due to intimidation, distress, or dependency.
Step-by-step explanation:
The undue influence defense in the execution of a will is triggered when there is suspicion or evidence that the person making the will, known as the testator, was under the presence of manipulation or coercion that overrode their free will when creating or modifying their will.
This manipulation typically originates from someone who stands to benefit from the will's provisions. Undue influence can be suspected in several scenarios, such as when the testator was experiencing some form of intimidation or distress, if they were frail to the point of dependency on the care of another, or if they had the potential to bestow a large inheritance, thereby giving someone close to them an incentive to exert influence.
To prove undue influence, a court will inquire what was happening when the individual wrote the document, including any relevant circumstances such as the individual's mental state and whether there was any sort of intimidation, distress, or dependency that could have compromised the voluntary expression of their intent.