Lieutenant Colonel Sir John Mansel Miller, GCVO, DSO, MC (4 February 1919 – 17 May 2006) was a British Army officer and equestrian who served as Crown Equerry to Queen Elizabeth II from 1961 to 1987.

[4] He was awarded the Military Cross (MC) in December 1944,[5] while serving as a major commanding a company in the 1st Battalion, Welsh Guards, with the citation noting, "that in the North Western Europe theatre of operations, after D-Day, in the face of heavy shelling, he kept his beleaguered men together, continually exposing himself to enemy fire, with complete disregard for his survival.

"[2] In March 1945, Miller was awarded the Distinguished Service Order for "re-establishing, again at great risk to himself, two companies of his regiment, scattered after a fierce enemy tank attack.

[2] Horses formed an integral part of Miller's childhood at the family estate, Shotover House, where he rode with the South Oxfordshire Hunt.

In 1972, he was a member of the first-place British team at the Equestrian World Driving Championships in Münster, where he also claimed an individual silver medal.

The princess royal's eventing career began with the horse Purple Star, a foal among seven born to Stella, Miller's favourite mare.

Miller helped oversee the princess's progress when she began riding Doublet, her partner in winning the 1971 European Eventing Championships.