Grosvenor Hotel, London to Denis Conan Doyle, Crowborough; "Dear old boy; I can't find paper so I write on an envelope"

Letter (undated) written on the front of an envelope to author's son Denis who was attending Beacon School in Crowborough; device of the Grosvenor Hotel on envelope flap; two of the accompanying empty envelopes are addressed to Master Denis Conan Doyle, Beacon School and marked "Local"; postmarked dates are 1921 and 1922; the 3rd envelope, bearing the Grosvenor Hotel device on its flap, is addressed to Mast. D. Conan Doyle, Beacon School, Crowborough; postmarked date illegible.