"Guernica" painter (7)
I believe the answer is:
picasso
'guernica painter' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for picasso that I've seen before include "Pablo . . . . . . ., great Spanish artist of 20th century" , "Spanish cubist painter" , "pioneer of Cubism" , "Spanish painter and sculptor" , "Pablo -, artist (Guernica)" .)