From Wikipedia:
"Alfonso was the object of diplomatic contacts from the empire of
Ethiopia. In 1428, he received a letter from
Yeshaq I of Ethiopia, borne by two dignitaries, which proposed an alliance against the
Muslims and would be sealed by a dual marriage that would require the
Infante Peter to bring a group of artisans to Ethiopia where he would marry Yeshaq's daughter.
In return, Alfonso sent a party of 13 craftsmen, all of whom perished on the way to Ethiopia.
[4]He later sent a letter to Yeshaq's successor
Zara Yaqob in 1450, in which he wrote that he would be happy to send artisans to Ethiopia if their safe arrival could be guaranteed, but it probably never reached the Emperor."
So in OTL in the 1400s the King of Aragon received a double marriage proposal for two of his kids with the Ethiopian Empire. One son with one daughter and one daughter with one son. His response never made it back to Ethiopia sadly and the son in question died in Italy in his 30s. What if the double wedding marriage alliance between Aragon and Ethiopia had gone through?