The Black Prince's Ruby (actually a spinel, not a ruby) is the large red stone found on the front of the Imperial State Crown of the United Kingdom. This stone is the second oldest stone on the crown, and is believed to have been worn by two different English kings in two notable battles. Name either notable battle, one in 1415 and the other in 1485, in which the king at the time supposedly wore the spinel (giving kings wearing this gem a 1-1 record in battles).
Battle of Agincourt or Battle of Bosworth Field