The first clear act of hostility was carried out in December 1383 by the faction of John (João), the Grand Master of the Aviz Order (and a natural son of Peter I of Portugal), with the murder of Count Andeiro. This prompted the Lisbon merchants to name him "rector and defender of the realm". However, the Castilian king would not relinquish his and his wife's claims to the throne. In an effort to normalize the situation and secure the crown for himself or Beatrice, he forced Leonor to abdicate from the regency. In April 1384, in Alentejo, a punitive expedition was promptly defeated by Nuno Álvares Pereira, leading a much smaller Portuguese army at the Battle of Atoleiros. This was an example of the use of the defensive tactic of forming an infantry square to repel cavalry, reportedly without any casualties to the Portuguese.