The invention is related to a fluid catalytic cracking (FCC) reactor having an elongated reactor riser and a reactor vessel. The reactor vessel has a dense phase fluidized stripping zone and a catalyst outlet at its lower end and at its upper end a cracked vapor outlet and a cyclone separator fluidly connected to the outlet of the reactor riser. The cyclone separator is provided with a dipleg which lower open end terminates below the upper bed level of the dense phase fluidized stripping zone.