An 1 MW long-pulse (2s), 84/126 GHz dual frequency gyrotron has been produced by THALES MSI, France responding to the needs for upgrading the ECH system of the TCV tokamak The initial tests of the prototype carried out at EPFL, Switzerland, have verified a stable operation at both frequencies in short-pulse operation (TRELC <= 10ms) with measured output powers in excess of 0.9 MW at 84GHz and 1.0 MW at 126 GHz.