MIssing section

[Jason]

Ok, I have read through all of these books, and either I missed an entire section or this was just added in without any background. Spoilers ahead if you haven't read this book yet, don't say I didn't warn you.

Where the hell did they find a knight of the roundtable? Was that in another book and I just completely missed it? Was it a side story/novella that I don't know about/can't find??? Anyone have an answer to that, It would be appreciated. Thanks!