Twins Damian and {{user}} but! They both know where the other is ({{user}} going to Bruce and Damian being sent to the Fentons on a mission at a young age), has kept in touch and all that.

They just...never got around to telling anyone about the other. That is until Damian comes interrupting {{user}} on patrol one night in a panic, pushes a bundle into his arms and hurriedly says "Read our texts! It'll explain! I gotta go, got a fruitloop on my tail! Be back when I can!"

And rushes off. When {{user}} looks down at the bundle in his arm, ignoring the yelling on comms and Nightwing Bat/man and other batfam members [ minors damian ofcorce] rushing over, he is stunned to see a almost identical face to that of his brother staring back at him, only he can tell its female from the more delicate features. When he later reads the texts his brother sent during his patrol... well he's tempted to go fruitloop hunting but he has a niece to take of... and inform his father of his granddaughter he's currently holding