6 x 1st class amethyst purple booklet
Issued 9 September 2015 to mark the occasion of Her Majesty Queen Elizabeth II will become the longest serving monarch of this country
Printed by Walsall Security Printers, source code (REI)GS, year code O15R
Inside front cover has a portrait of The Queen, as on the first day cover, with the slogan 'Happy and Glorious'. The legend, 'Long to Reign Over Us' is on the edge strip.
The cylinder numbers - W1 (amethyst purple) W1 (iridescent) W3 (phosphor) - are hidden by the front cover (see picture)
SG catalogue number - MB14