9 September 2015 - 1st class Amethyst Purple
Issued to mark the occasion on which Her Majesty Queen Elizabeth II will become the longest serving monarch of this country.
The retail book of 6 x 1st was issued on the same date as the miniature sheet and counter sheet.
These stamps have year code 015R under the chin, and source code (REI)GS behind the neck. The Source code on these stamps is partly hidden by the security cuts.
SG number probably U3745 (renumbered from 3746)