Wait, is Eternals bringing again a significant MCU character?
Fortunately, the Eternals saga spans thousands of years. So if Thanos actually appears in the movie, it’s logical to assume that they’re flashbacks. And it’s not like being treated with a shoehorn, because Thanos is closely associated with the Eternals in the comics, especially the Titanian offshoots. He is the son of the Eternal A’lars and Sui-San, and his brother is Eros of Titan. So Thanos is a part of Eternal, and the reason he looks so monstrous compared to other members of this breed is that he has different genetics too. We also visited Titan, Thanos’ homeworld, in Avengers: Infinity War, though it was long dead after being devastated by overpopulation and natural resource scarcity.