Pius XII was an antipope, as was Pius XI, who made the pact with Mussolini. Benedict XV, before them, who is on public record as uttering four different heresies, who fought for Modernism and squelched its enemies, was also an antipope.
Pius X, on the other was was the Vicar of Jesus Christ and if he were here right now, he would say "See, I warned you."