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More than 20 crystalline and amorphous phases have been reported for ice sofar. This extraordinary polymorphism of ice arises from the geometricflexibility of hydrogen bonds and hydrogen ordering, and makes ice a uniquepresence with its universality in the wide fields of material and earth andplanetary science. A prominent unsolved question concerning the diversity iswhether a hydrogen-disordered phase of ice transforms into only onehydrogen-ordered phase, as inferred from the current phase diagram of ice,although its possible hydrogen configurations have close energies. Recentexperiments on a high-pressure hydrogen-disordered phase, ice VI, revealed anunknown hydrogen-ordered form ($\beta$-XV) besides the known ordered phase, iceXV, which would be a counterexample of the question. However, due to lack ofexperimental evidence, it has not been clarified whether $\beta$-XV is adistinct crystalline phase. Herein we report a second hydrogen-ordered phasefor ice VI, ice XIX, unambiguously demonstrated by neutron diffractionmeasurements. The phase boundary between ice VI and ice XIX shows that ice VIcontracts upon the hydrogen ordering, which thermodynamically stabilizes iceXIX in higher-pressure region than ice XV because of its smaller volume thanice XV. The pressure-driven phase competition between hydrogen-ordered phases,also theoretically suggested in other ice polymorphs, can induce hydrogenordering of ice in different manners. Thus, this study demonstrates a hithertoundiscovered polymorphism of ice.

New diversity form of ice polymorphism: Discovery of second hydrogen ordered phase of ice VI