The simple answer to what happened with the Spanish Crown Jewels: they’re gone.
Some of the jewels were destroyed in a fire. Others were stolen or went missing during Napoleon’s invasion. Rumors indicate that some others are hidden and lost at the Royal Palace in Madrid.
Alfonso XII commissioned a new crown and scepter, but they disappeared during the Civil War.
No Spanish King has been crowned since the 1300’s. Instead, they are “proclaimed.” As with the current monarch, King Juan Carlos, a crown is displayed during the ceremony.
But the above crown, simple in appearance and construction, is not an official “Crown of Spain.” It was commissioned for a royal funeral in the 1700’s and last seen publicly in 1981.
The true Crown of Spain is not a real object but a heraldic symbol.
Generally, the jewels worn by Spanish royals are private.
One of the tiaras belonged to Queen Maria Christina of Austria. Another was a gift from German Emperor Wilhelm II to Princess Victoria Louise of Prussia, Queen Sofia’s grandmother.