Mary, Queen of Scots's grandmother was Elizabeth's father's (Henry VIII) older sister. Since Elizabeth had no children, the monarchy was to pass to Mary, Queen of Scots upon Elizabeth's death. However, Mary was found guilty of trying to overthrow Elizabeth and was therefore executed. Because she was Catholic, and Elizabeth (and England) was Protestant, this greatly angered King Philip of Spain. He also felt he had a legitimate claim to the English throne since he was married to Elizabeth's sister (another Mary, who died years earlier). All of these events angered King Philip.