abubaker deghayes , 46 , has left his home in brighton in an attempt to rescue his son amer .
the 21-year-old has been fighting for the organisation jabhat al-nusra , a group affiliated with al-qaeda , who are battling the islamic state and syrian forces .
mr deghayes two younger sons were killed last april after suffering a bullet wound to his stomach and jaffar , 17 .