Another theory holds that the island found by De 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 ) .
Another theory holds that the island found by De 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 under the command of Estêvão da Gama on 30 July 1503 .