This is a gorgeous shirt from Nat Nast.

Made of silk and cotton, it's a reddish purple.

The shirt has a straight collar, two-button barrel cuffs, two chest pockets with buttons, slim fit, and a squarish tail.

This  shirt is in MINT condition. 

I have measured the shirt and: 

The neck measures 16.5 inches from button to button hole.

 The sleeve length is 34/35inches from mid-collar to the end of the cuff. 

Across the back, laid flat, the shirt measures 23 inches armpit to armpit and 31 inches from the collar seam to the bottom of the back tail.