Magnificent fish mate,very well done indeed. I've landed many wild rainbows from the Wye in the 1 and half lb envelope,and they scrap like the devil himself....God knows what this specimen fought like!
What fly did he take? What area were you fishing? Seen many beasties like this one (Browns too) in the 5,6,7 lb range queuing up in the town to take Bakewell tart tossed to 'em by the tourists!
Maybe 4 layers of foam superglued together on a b400 then shaped into a tasty looking cube - off white(pastry) beige(filling) red(jam) dark brown(crust) ?