Why did Joseph I of Portugal want to marry his daughter to his grandson?

In 1777, Joseph I, king on Portugal, on his deathbed, made sure that his youngest daughter, Benedicte, would marry the son, also called Joseph, of his eldest daughter and heir, Maria.

I came across this fact today, and it mystifies me. The grandson was expected at the time to eventually become king of Portugal himself, after his mother (but he died young and didn’t). At the time, heirs were generally married to princes and princesses from other kingdoms, to create alliances. So, Joseph marrying a Portuguese woman would be in itself a bit unusual. But a member of his own family? His aunt? I would assume that marrying one’s aunt would have been considered unacceptable at the time. I know that exceptions to this kind of rules would have be made for sovereign and their heirs, but usually for closely related cousins, not aunt and nephew. And when there were very good reasons for the marriage. What could have been the imperious reason to marry Joseph to his aunt?

I failed to find any explanation on French or English websites, and I don’t speak Portuguese (the Portuguese wikipedia article at least doesn’t give any explanation, either). I thought maybe a scandal that needed to be immediately covered up, but there was no birth or stillbirth immediately after the marriage. Maybe to reunite two competing claims on the crown? Nope, there’s no hint that there were any dispute.

Does anybody have a clue why this marriage took place?

I would also note that at the time of the marriage, Joseph was 15 and his aunt 31. Which is another mismatch, if only because you want the likely heir to the crown to have children, and for this reason should want to marry him to a younger woman. The whole thing really doesn’t make any sense to me.

Immitating the Spanish Hapsburgs, perhaps. To keep the power within the family, the Hapsburg heirs usually married their first cousins or nieces. Occasionally they’d marry outside, such as Philip II marrying Mary Tudor, but marrying within the family was their usual practice.

I don’t know this specific case, but his daughter was already married to his brother. The Da Poyle bloodlne has been clean and pure for a thousand years!

Didn’t the Hapsburgs eventually get to a guy whose only distinct sentence was, “I am the Emperor, and I want noodles!”?

The 1770s were kind of late for this kind of close-kinship marriage, but there were 16th-century precedents. For example, after the death of Queen Isabella, Ferdinand married Germaine of Foix, the granddaughter of his sister Eleanor and so his own great-niece. There were several other uncle-niece and at least one nephew-aunt marriages among the less prominent noble families of that era; the Pope would hand out dispensations.

OK, so it seems that this wasn’t as surprising or unusual as I thought it was. I didn’t know that dispensations would be easily granted for so close blood relationships, either. That’s one of the things that was puzzling me, in fact : how could they marry in church?

You’re probably thinking of Carlos II, famously victim of heavy inbreeding. Even though I never heard about this particular sentence.

He’s thinking of Ferdinand 1 of Austria, and while he said something similar (“I am the Emperor and I want dumplings!” when apricots were out of season), Wikipedia reports that his major issue appears to have been a very bad case of epilepsy and a speech impediment. His diaries reportedly show that he was compos mentis, but between the problem with speaking and something like 20 seizures a day, he had problems ruling effectively and eventually abdicated.

The century long inbreeding of the Hapsburgs showed in their famous jaws.

“[His body] did not contain a single drop of blood; his heart was the size of a peppercorn; his lungs corroded; his intestines rotten and gangrenous; he had a single testicle, black as coal, and his head was full of water.” !

Hmm. Sounds like Cirsei describing baby Tyrion to Oberyn.

Or Daenerys’ bat winged baby.

Auntie’s marryin’ her close relation
Pope is givin’ her a Dispensation
Dis, Dis, Dis, Dispensation!

To forestall an uncle-niece conflict (or even war) over the succession.

This was a very real concern in any monarchy which allowed (maybe–the uncle will always argue the point) succession to pass to or through women. In the years after Joseph’s death, Spain would see the incredibly destructive uncle-niece Carlist Wars, and Portugal itself would see an uncle-niece war between Maria II and Miguel.