This is a mens short sleeve shirt by Prada for their Linea Rossa line.

Size: Medium 

Color: Grayish Blue

Made in Italy

Measurements:

armpit to armpit: 20 inches

top back collar to bottom edge: 24 inches

sleeve: top shoulder seam to sleeve edge: 7 1/2 inches

No label on the inside, so I don't know the fabric or care information.