qnli question: What navigator discovered the island? sentence: Another theory holds that the island found by da Nova was actually Tristan da Cunha, 2,430 kilometres (1,510 mi) to the south, and that Saint Helena was discovered by some of the ships attached to the squadron of Estêvão da Gama expedition on 30 July 1503 (as reported in the account of clerk Thomé Lopes).