Disclosed is a gas turbine engine comprising: a low pressure spool having a low pressure compressor and a low pressure turbine connected by a low pressure shaft; a reduction gear train having a sun gear, a carrier having a plurality of planet gears attached thereto, and a ring gear, wherein the sun gear is driveably connected to the low pressure shaft, and either of carrier and ring gear provides an output drive connected to a propulsive fan; wherein the connection between the low pressure shaft and the sun gear includes a flexible drive shaft having serially connected concentrically nested first and second input shafts between the low pressure shaft and sun gear.