In this article, we study symmetric designs with λ prime admitting a flag-transitive and point-primitive automorphism group G of almost simple type with socle X. We prove that either D is one of the six well-known examples of biplanes and triplanes, or D is the point- hyperplanedesignofPG(n−1,q)withλ = (qn−2−1)/(q−1)primeandX = PSLn(q).
