There is a reason Mary earned the nickname "Bloody Mary." During her short five-year reign she attempted to reverse the Reformation and restore property back to the Roman Catholic Church. This, naturally, involved killing a lot of people, as sensationally documented in Foxe's Actes and Monuments of the Latter and Perillous Dayes (more commonly called Foxe's Book of Martyrs). This formal invitation wasn't to the kind of party anyone wanted to attend.
The intended guests didn't have to wait much longer in exile. Mary died two years later and Elizabeth I assumed the throne and made it safe for these particular nobles to visit court again.
We are still cataloging the letter, but we will put a link here when it is ready. It pairs nicely with our 1563 first edition of Foxe's Book of Martyrs--just ask for Presses D334f.