That’s the usual story and it’s not wrong, per se. But, as with much in history, there’s more.
Henry liked sparklies. Was always on the look-out for a new and nifty title, or gee-gaw to add to his collection. In 1512, he petitioned Julius II to award him the title possessed by Louis XII, “Most Christian King” (you didn’t just call yourself something like that; it was awarded). Not sure if “Most Christian” was a singular, zero-sum title, but Julius did award it to Henry, and, for good measure, secretly gave him the French throne. All he had to do to claim it was to defeat Louis in the then on-going unpleasantness between the Holy League and France. That part never happened, though Henry tried. But Henry got his “Christianissimus”.
In 1515, Henry wanted something else to pad his resume. Various ideas were passed around: “Protector of the Holy See”, maybe “Defender”, from the English side. The first was turned down because it already belonged to the Holy Roman Emperor, the second was the property of the Swiss. Some in Rome countered with “King Apostolic” (interesting combination) or “Orthodox”. The Pope vetoed both. In 1516, the title of “Defender of the Faith” was proposed from England. Leo ignored it, and Henry gave up until May, 1521, when Wolsey wrote once again to Rome, asking for a pretty for Henry. Leo passed it to a committee of Cardinals. Forthcoming were suggestions:
“Rex Fidelis”, “Orthodoxus”, “Ecclesiaticus” ,
“Protector”, “Anglicus”
When the Cardinals inquired just why Henry warranted another honor, the part he had played fighting for the Holy See against Louis, 9 years before, was mentioned. And there was the Assertio Septem Sacramentorum adversus Martinum Lutherum, of which Rome had heard (it was in draft in May 1521, printed in July, sent to Rome in September, after the Cardinals had been considering the matter for a few months. And it was at least partially Henry’s work. Probably). So, before the Assertio was received and presented to Leo, (his copy bound in cloth-of-gold, hand inscribed to Leo, the 27 other copies more mundane), a list of titles for Henry to choose from was shipped to England.
The Assertio probably tipped the scales. About the time it was presented to Leo, Henry chose the same title that had been suggested by England 6 years before: Defensor Fidei . Leo granted it six weeks after he received the book. Doubtless directly inspired by the Assertio, some cardinals then wanted to add a flourish such as Gloriosus or Fidelissimus, but Leo vetoed it.
So Henry got his sparklie, partially because of the Assertio, partially because of the Holy League, partially because he was a pain in the neck. It was intended as a title for him personally, though he thought it was hereditary. Parliament thought it looked nice, and attached it to the Throne, in 1543. Mary took it off, in her Second Act of Repeal, Elizabeth put it back, and it’s there now by legislative fiat. Hence, the title attached to the British Monarchy today is not really the same as the one Henry bore. It’s a gift from Parliament. Just uses the same words.
History is full of interesting stuff.