His marriage in 1554 to Queen Mary I Tudor of England would not count as an enthroned king marrying the daughter of another enthroned king, since Henry VIII by then had been dead for seven years.

However, despite the fact that his father (Holy Roman Emperor Charles V) was still living, and he was not yet the king of Spain, he nevertheless was the king of Naples and Sicily. So had his bride on the occasion been only a princess, as opposed to a queen regnant, then that marriage would count.

I personally can't think of other examples than the ones mentioned in this thread; but there may be others, especially in the distant past.

However, royal weddings long ago could not have been the same as what they would become in more recent centuries, in that they probably weren't the grand events we have come to know. Even if they involved the marriages of sovereigns or direct heirs, the ceremonies may well have been largely private events.

Also, marriages by proxy used to be a common practice -- especially in long-ago days, when royal unions were typically arranged. So it may be that one didn't necessarily see a king, even if still living, escorting his daughter up the aisle as the father of another king's bride.

The custom of a father *giving away* his daughter at her wedding is probably not an ancient or universal one.