Warning! Spoilers for Eternals: Thanos Rises #1 by Marvel Comics below
Marvel's Eternals are keeping a secret from Thanos that's so potentially dangerous, it could lead to the destruction of Earth. In Eternals: Thanos Rises #1, it's revealed that the Mad Titan's parents are being kept in exclusion, and the only way for them to be freed is the destruction of Earth. Thanos, who wants nothing more than to kill them again, isn't aware of the secret, at least not yet.
Thanos has always had a rocky relationship with his parents, Mentor and Sui-San. Their second-born child was born a monster as the Deviant gene significantly altered his appearance. It led to his mother trying to kill him after giving birth and later dying at this hands. Thanos also killed Mentor following an encounter where the father told his son he wished he could have killed him himself after seeing what he became.
In Eternals: Thanos Rises by Kieron Gillen, Dustin Weaver, Matthew Wilson, and Esad Ribic, readers are taken back in time, where the ancient race reset their minds following a Civil War. To prove Eternals can be born and not created, Mentor is given a chance to find a partner and create life through natural means of reproduction - something the ancient race long opposed. After Mentor met Sui-San on Titan and received Quantum Bands allowing them to reproduce, Eros would be born. However, their second child, Thanos, became a monster who would later kill them both. After reawakening after death, Mentor reports his findings that the Eternals should not breed, and he's thrown into exclusion. Mentor and Sui-San are kept in exclusion until Earth is destroyed - meaning if Thanos ever found out about them, he could destroy the planet to get to his parents.
It's one hell of a secret to keep from Thanos. The Mad Titan has a strained relationship with his parents, and if he knew they were still alive and held in exclusion, he would have no second thoughts about destroying Earth to get to them. Mentor attempted to show the Eternals they could reproduce without the Great Machine, essentially costing him his life. He has two options he can't control. Either he rots away in exclusion where he's forced to learn about every death Thanos has caused or he's eventually freed when his son destroys Earth and comes for him. He's eternally damned no matter what.
Marvel's greatest heroes better hope the Eternals (or the Deviants) don't tell Thanos of the secret of his parent's actual whereabouts. Otherwise, it could lead to the destruction of Earth and one of the greatest wars in Marvel history. Eternals: Thanos Rises #1 is in comic book stores now.
