UPDATED: G.R.R. Martin denies rumor he already finished the books but made deal with showrunners not to publish until end of show

[haxxiy]

Debunked by the man himself: http://georgerrmartin.com/notablog/2019/05/13/idiocy-on-the-internet/

He seems quite pissed off about it, too. Should update OP, in any case.