The tiara came from the Medinaceli family who donated or loaned it to the convent where it was used to adorn a statue of the madonna, afaik. There is a portrait of Angelea Perez de Barradas y Bernuy, Duchess of Medinaceli, wearing it with rubies. And the fact that something was used in a catholic church or convent doesn’t mean that this artefact is fake. Some old churches still preserve enormous treasures of gold and precious gems.
It would amaze me if Franco really bought something fake. He seemed rather fascinated with splendid jewels that I assume that he would have estimated the jewels by a professional before buying. But that is only my assumption of course.
Queen Fabiola started to wear the wreath version of the tiara in 1963. But she wore the coronet version again in 1964 at a State Visit to the Iran. Unless the date for that Iran Visit is wrong, the tiara was not changed for good and Fabiola changed it back to the coronet at least once.
I hope that more information will be disclosed as soon as the distribution of the heirlooms has been finalized. It’s a really intriguing question.