#i believe catherine argued that the short life of henry nyp proved otherwise but anyway i do wonder if either were aware of this precedent

[fideidefenswhore]

i recently read and confirmed elsewhere (on tudorhistory q/a ... of all things) that there was actually a (single, afaik) precedent for a royal marriage wherein the widow married her husband’s brother, it was however very different in circumstance to the marriage of catherine and arthur and subsequently henry which is maybe why it was never brought up precedentially by either side....

On 18 October 1319 the wedding ceremony between James of Aragon and Eleanor of Castile took place. James, according to the chronicles of the time, refused to give the kiss of peace during the ceremony, and James II had to do it.[2] After the ceremony, officiated by the Archbishop of Tarragona, the bridegroom again transmitted to his father his desire to renounce his rights to the throne and enter a convent. After the wedding ceremony, and after a discussion with his father, he fled on horseback, leaving his wife abandoned, and in December 1319, renounced his rights to the throne of Aragon in the Convent of San Francisco of Tarragona. Immediately, he took the habit of the Knights Hospitaller in the Convent of Santo Domingo of the same city.[2]

Alfonso, King James II's younger son, was proclaimed heir apparent. The rejection of Eleanor could have caused serious diplomatic incidents between the Castilian and Aragonese courts. James II informed Eleanor's grandmother, Queen Maria, about his regret for the actions of his eldest son, incomprehensible to him. During the spring of 1320 Eleanor remained lodged in the city of Tortosa; during her stay there, James II and Alfonso became aware that the younger James planned to recover his wife and his rights to the throne, and the conspiracy was thwarted by his father.[3]

After her stay in Tortosa, Eleanor lived in the cities of Zaragoza, Calatayud and Ateca, from where some Castilian ricohombres returned her to the Kingdom of Castile and León.[4] Once in her homeland, Eleanor retired to the Abbey of Santa María la Real de Las Huelgas, although she never took the veil.[5] In early 1325, King Edward II of England proposed the marriage of his eldest son, Edward, with Eleanor, and sent his proxies to negotiate the terms of the wedding by charter dated 6 February 1325. The union never took place due to Edward's deposition.

so...never lived together, never so much as even shared the same bed the night of the wedding, not to mention he takes orders before he can do any of these things, and abdicates (although apparently he gets cold feet/buyers’ remorse later...). very different case, but, funnily enough, eleanor does have sons by her previous husband’s brother after their marriage:

In Ágreda in January 1329 the betrothal between Eleanor and King Alfonso IV of Aragon was signed, and the wedding ceremony took place one month later, on 5 February in the Church of San Miguel de Tarazona. The ceremony was attended by King Alfonso XI of Castile and King James II's children, Maria, John, Peter and Ramón Berenguer. Alfonso IV gave his new wife the city of Huesca and other villages and castles belonging to the Aragonese crown.[4] This marriage improved relations between Castile and Aragon in a renewed alliance formed with the aim of reconquering Granada. The Kingdom of Aragon had breached several marriage agreements, returning to Castile several princesses after breaking off engagements, and this union put an end to the practice.

Eleanor became a disruptive influence in Aragon, plotting to advance the interests of her own sons over those of her stepson, Peter, born from Alfonso IV's first marriage with Teresa d'Entença, Countess of Urgell, who died in 1327. She convinced her husband to consent to make significant territorial donations to the children born to them, Ferdinand and John. Alfonso IV was generous and on 28 December 1329, he granted Ferdinand the Marquisate of Tortosa and the cities of Albarracín, Orihuela, Callosa, Guardamar, Alicante, Monforte, Elda, La Mola, Novelda and Aspe.[7] Eleanor's younger son John also received several lordships: Elche, Biel and Bolsa.

These donations made by Alfonso IV diminished the territorial patrimony of the crown and mainly affected Peter, producing a climate of resentment in the Aragonese court. Because of this the nobility was divided into two camps. One of the two sides was in favor of Queen Eleanor and her sons, and the other defended the prerogatives of Peter and his full siblings. When the King granted his son Ferdinand the cities of Xàtiva, Alzira, Sagunto, Morella, Borriana and Castellón de la Plana, all located in the Kingdom of Valencia, the local subjects protested, and for this reason the King decided to revoke these last donations

although...

Her youngest son, John of Aragon, was assassinated in Bilbao on 12 June 1358 by order of his cousin the Castilian sovereign,[10] and one year later (March/April 1359), she was murdered in the castle of Castrojeriz by order of her nephew.[5]Four years later, in 1363, her oldest son, Ferdinand of Aragon, was assassinated in Burriana by order of his half-brother, King Peter IV.[11]