Complex sentence: He revealed to them that Django and Marya Maximoff were their true parents--implying that the twins are actually the lost Ana and Mateo Maximoff--and that they were not mutants but had been experimented on by the High Evolutionary.
Split into simpler sentences: He revealed to them that Django and Marya Maximoff were their true parents, implying that the twins are actually the lost Ana and Mateo Maximoff. He also told them the truth where they were supposedly not mutants, but they had been experimented on by the High Evolutionary.