In 1548, when she was only 15 years old, Elizabeth was under suspicion of having illegally agreed to marry Thomas Seymour. The house and her servants were seized by Edward VI's agent, Robert Tyrwhit, and she was interrogated there. She successfully defended her conduct with wit and defiance. Seymour was executed in 1549 for numerous other crimes against the crown. After her two months of imprisonment in the Tower of London by her sister, Queen Mary, Elizabeth returned to Hatfield. The Queen Elizabeth Oak on the grounds of the estate is said to be the location where Elizabeth was told she was queen following Mary's death, but is considered unlikely as Mary died in November. In November 1558, Elizabeth held her first Council of State in the Great Hall.