Jammu and Kashmir's erstwhile royal family member and Congress leader Karan Singh's son Ajatshatru Singh Sunday joined the BJP, a move that is expected to strengthen the party in the state.The younger son of Karan Singh and grandson of Maharaja Hari Singh, Ajatshatru joined Bharatiya Janata Party (BJP) in the presence of party president Amit Shah.He was earlier in the National Conference and a sitting member of the state legislative council from the Nagrota seat.