Ancient Covenant

The Ancient Covenant was a mutual pact between the Eternals and the Chronovores. Among other things, it forbade unions between the two species. Elektra and Prometheus violated the Covenant to sire the unique Eternal/Chronovore hybrid Kronos, who their parents hoped would become their unified races' hope against Nyarlathotep and his kind. (PDA: The Quantum Archangel)