At the Trial of Seven at Ashford, which Prince killed his brother?

Prince Maekar fought for the Accusers, and Prince Daeron for the Defenders.

Prince Maekar delivered a blow to the head with his mace that would lead to the death of Prince Baelor. Prince Maekar did not remember the blow that broke Prince Baelor's skull, and feared he would always be known as a Kinslayer.