100% Linen short sleeve shirt, River Island S (poss. M) (Corstorphine EH12)

100% Linen short sleeved shirt. I bought this new in River Island, probably over twenty years ago. A nice light summer shirt. Labelled Small, it measures 20" chest width (pit to pit) and 28" back length (collar lower seam to hem), measurements taken with the shirt fastened and laid flat. I often take a medium and it fits me. Just washed but needs to be ironed as seen in photos.