Suddenly They Have A Sibling

Dru (Despicable Me)

Sam (Uncharted)

They are never mentioned at the beginning of a series but at some point the main character of the story suddenly has a sibling who is the catalyst for the next adventure.

I won’t say I hate this trope as it can work if done right but I do feel it’s one of those fallback ideas for when nothing else works. Don’t have any reason for the protagonist to go on this adventure? Boom, long lost sibling shows up!

I guess bonus points if at any point the siblings are at odds with each other.