Thane is the secret Inhuman son of Thanos. After a descendant Inhuman tribe ran afoul of Thanos and his army, one Inhuman woman returned home pregnant with Thanos' child.

How many sons does Thanos?

Raised by Thanos

Thanos adopted six known children, Ebony Maw, Proxima Midnight, Corvus Glaive, Cull Obsidian, the Zehoberei Gamora, and the Luphomoid Nebula, and trained them in the ways of combat, turning each of them into a deadly warrior.

Who is Thanos biological daughter?

Gamora is the adopted daughter of Thanos, and the last of her species. Her powers include superhuman strength and agility and an accelerated healing factor. She also is an elite combatant, being able to beat most of the opponents in the galaxy.