The prospective purchaser, prospective mortgagee or any other person interested in any land upon which a nonconforming use or structure exists may apply in writing for the issuance of a certificate certifying that the use or structure existed before the adoption of the ordinance which rendered the use or structure nonconforming. The applicant shall have the burden of proof. Application pursuant hereto may be made to the administrative officer within one year of the adoption of the ordinance which rendered the use or structure nonconforming or at any time to the Board of Adjustment.