Summary: During the century-defining duel in 1945, the powerful magic wielded by two wizards as they fought twisted space and time. A nine-year-old blond boy with a milk-white complexion, happily playing all over the Bagshot family home in Brazil, was swapped into the dueling arena. Meanwhile, the real old Dark Lord Gellert returned to Godric's Hollow, a place full of memories from half a century earlier, where he met an eleven-year-old little Dumbledore.
"Want to make a bet, Dumbledore? I'll raise him to be my most prized follower."
"I won't let this Gellert become the next Dark Lord. Trust me, Grindelwald."
It's really just a story about both of them raising a child, and the two of them muddling through a romance with their former lover in a little one's body (?). The setup is that the two adult wizards can briefly meet through a shard of the Mirror of Erised every full moon, though their conversations are usually quite unpleasant.
Theme: Age-gap shenanigans, GGad, enjoy the ggAD to your heart's content.
Hagrid is Tom's younger brother. . . Neither of them were born now?