Imagine Finwe's confusion when Maglor introduces Elrond as Finwe's great grandson. But moments later, Turgon comes up to them and introduce himself as Elrond's great grandad.

Bonus:
Maglor: this is my son, Elrond, so he'll be your great grandson, Grandpa!
Finwe: *happiness*
Turgon, passing by: Oh, yeah, that's my great grandson.
Finwe: *visible confusion*

Thank you return_of_the_king for the bonus!