AT the end x IN the end

AT the end of : as the opposite of "at the beginning of"
I'll meet you here at the end of the concert.
At the end of the class, the teacher said she wanted to talk to me.
I'll have an answer at the end of the day, ok?

IN the end of: as a synonym of "finally"
In the end,  they shook hands and made up.
In the end, it'll all be the same thing.
In the end, we decided not to buy it. 

source: Inglês na Ponta da Língua