Feast of Crows..."Who is Pate?"- And a sort of pseudo review/meta

So, I finally finished George RR Martin's Feast of Crows and I've got a question for anyone who has read and finished this book.

Who is Pate? Samwell Tarly meets Pate or Alleghris/The Spinx in the final chapter.
And yes it neatly echoes the first chapter or bookends it.
( spoilers for Feast of Crows )