This is a pair of Montserrat Princess Anne Royal Wedding stamps.  They were used as POSTAGE DUE on a cover from French Guyana in 1974.

The cover has a slogan cancel on it to Radio Antilles.  This is VERY RARE!

If you like what you see, come check out our store!  We offer a wide variety of stamps, covers, and other items for all your philatelic wants and needs!