Cape of Good Hope 1863 Rare De La Rue 1/- Triangle Franking

1863 SIMONS TOWN to SCOTLAND: Small format envelope franked De La Rue 1/- BRIGHT EMERALD GREEN (SG 21) endorsed "Per RMS Briton". Adhesive has rich colour; margins touching to full however overall giving even appearance, pressed crease. Glasgow arrival DE 23 63 on reverse. The envelope somewhat restored (cleaned, pressed) to give a very presentable example of this rarity, few covers bearing the De La Rue 1/- exist. Signed: A Diena; Photo-cert: PFSA. See clickable image of certificate below.