De Son Tort is a French law phrase which means by his/her own tort or wrong. It denotes the breach of a fiduciary duty. This term is usually applied to a person who having no right to intervene with the affairs or estate of a person undertakes to do so, by acting as executor of the deceased. It is used in the two phrases executor de son tort and trustee de son tort. An executor de son tort is a person who, without legal authority, takes it on himself to act as executor or administrator as by acting or dealing with any of the decedent's property. A trustee de son tort acts similarly in respect of a living person's property.