A process for simultaneously heating and cooling of spent FCC catalyst during regeneration in a high efficiency FCC regenerator, one using a fast fluidized bed coke combustor. The coke combustor burns coke from spent catalyst in a turbulent or fast fluidized bed, and discharges catalyst and flue gas up into a dilute phase transport riser. Catalyst is separated into flue gas and a bubbling dense bed of catalyst. The coke combustor is heated by recycling hot catalyst from the bubbling dense bed and simultaneously cooled by a backmixed heat exchanger. Catalyst flows from the combustor to the cooler and is displaced back into the combustor by adding air to the catalyst in the cooler. Heating promotes rapid coke combustion, while cooling reduces thermal and hydrothermal deactivation of the spent catalyst. High superficial vapor velocities in the cooler promote heat transfer without disrupting flow in the fast fluidized bed coke combustor and without increasing catalyst traffic in the flue gas above the bubbling dense bed.