“Cum Ex Apostolatus Officio” was issued by Pope Paul IV on 15 February 1559. It focused on the validity of a prelate or Pope in the event they were in heresy or apostasy. This Papal Bull was issued Ex Cathedra, so it is valid in perpetuity. It’s out there on the web. The version I found is in Latin with an English translation. It’s very interesting.
Aha, thank you for that info!