VGFacts

In the post-game version of the Tower of London, there is a man in a prison cell William can talk to. Through the hints he gives about himself, he is likely Walter Raleigh, the man who claims to have found the "City of Gold", El Dorado. This is highlighted by the Large Spirit Stone he gives to William after exhausting his dialogue.

Sources:
https://www.youtube.com/watch?v=nZ29fMh9rUU

The video you linked is not available. Do you have another one?

EDIT: well, thank you.