On December 17, 1538, Henry VIII was formally and publicly excommunicated:
Bull against Hen. VIII., renewing the execution of the bull of 30 Aug. 1535, which had been suspended in hope of his amendment, as he has since gone to still further excesses, having dug up and burned the bones of St, Thomas of Canterbury and scattered the ashes to the winds, (after calling the saint to judgment, condemning him as contumacious, and proclaiming him a traitor), and spoiled his shrine. He has also spoiled St. Augustine’s monastery in the same city, driven out the monks and put in deer in their place. Publication of this bull may be made in Dieppe or Boulogne in Fiance, or in St. Andrew’s or Coldstream (? “in oppido Calistrensi”), St. Andrew’s dioc., in Scotland, or in Tuam or Ardfert in Ireland, if preferred, instead of the places named in the former bull Rome, Paul III.
Pope Clement VII had not published a formal Bull of Excommunication against Henry VIII; there was always hope that he would repent. When both Katherine of Aragon and Anne Boleyn had died in 1536, Henry was freed of all marital impediments, so his marriage to Jane Seymour and the successful delivery of a baby boy (Henry must have been so relieved when Edward survived the first few months and then a full year!), led to those hopes that he might return to the Catholic fold, give up his spiritual authority in England, and stop his dalliance with Reformed theology and religious practice. After Jane's death, Henry's marital prospects included some Catholic princesses, so there was again some hope. But then the destruction of shrines, the suppression of monasteries and friaries, and Henry's obduracy must have convinced Pope Paul III that the time was right to publish the excommunication.
Henry VIII had already upset the Pope and the Catholic Church by:-
-Annulling his marriage to Catherine of Aragon and marrying Anne Boleyn
-Declaring himself “Supreme Head of the Church of England
-Persecuting those who opposed the Acts of Supremacy and Succession
-Dissolving the monasteries
-His handling of the Pilgrimage of Grace
But the final straw was Henry’s attack on religious shrines in England, shrines that contained religious relics and that were visited by many pilgrims. One such shrine was that of St Thomas Becket (Thomas à Becket) in the Trinity Chapel of Catherbury [sic] (Canterbury) Cathedral, which was seen as one of Europe’s holiest shrines and was therefore a popular destination for pilgrims from all over Europe. In a meeting of the King’s Council on the 24th April 1538 a “Process against St Thomas of Canterbury” was decided. . . .
One treasure which was purloined by the King from the shrine was the Regale of France, a great ruby which was donated by King Louis VII, and Henry VIII had this made into a thumb ring for himself.
Such desecration of a place which many pilgrims, and the Catholic Church as a whole, saw as holy could not go unpunished and it was this final act which made Pope Paul III issue the Bull of Excommunication.
Note again, however, that Pope Paul III waited until almost the end of the year (from April to December) to finally issue the decree of excommunication. It was a signal to Henry's European foes, Frances I, King of France and Charles V, the Holy Roman Emperor, as Nancy Bilyeau explains here. England has always been part of an island, of course, but Henry's action against the shrine of St. Thomas a Becket was making it more insular than ever, cutting it off from the community of Europe more surely than the English Channel. St. Thomas a Becket and his shrine was for all Catholics in the world; Henry thought the shrine was his to dispose of as he wished.