These were on the one hand Henry of Trastamara, an illegitimate son of Alfonso XI of Castile from his relationship with his mistress Eleanor de Guzmán, and on the other Peter I (nicknamed The Cruel), a son of Alfonso XI from his marriage to Maria of Portugal.
These were Ferdinand I of Portugal (1345-1383), a great-grandchild of Sancho IV of Castile (through the female line), and John of Gaunt, Duke of Lancaster, married to a daughter of Peter I, Constance.
The French had signed a treaty with Castile on June 12 to assemble a naval expedition against England.
On the other hand, France had already negotiated with John of Gaunt in the spring to relinquish its claims to the throne of Castile.
In 1389, the Truce of Leulinghem was concluded between England, France, Castile, Scotland, Burgundy and Portugal.