1911 FIRST U.K. AERIAL POST WINDSOR PRIVILEGE ENVELOPE IN VIOLET TO HENDON. A fine example of the rare Windsor privilege envelope in violet, very minor soiling to 'Central London Sick Hospital, Collindale Avenue, Hendon' with KGV 1d Downey tied fine strike 'FIRST UNITED KINGDOM/AERIAL POST/WINDSOR' date stamp SP 16 1911Die 2. (Ref 141326.)