What is the ruling on one who denied the prophethood of one of the prophets out of ignorance, then learned of it; such as Seth (Sheth) and Joshua son of Nun?

The prophethood, the denial of which constitutes disbelief, is the prophethood of those prophets whose prophethood is agreed upon. This is like one who denies the prophethood of an agreed-upon prophet, not like Al-Khidr, Khalid ibn Sinan, Luqman, and others. The term "well-known" should be understood to refer to those whose prophethood has been unanimously agreed upon by Muslims.