Prince William extended his "deepst sympathy" to the relatives of 36-year-old James, who was a respected Army Lynx helicopter pilot and Warrant Officer who served with the elite Wild Cat Fielding Team, based at RNAS Yeovilton in Somerset.
The officer was specially selected to train the future King on a fast-track, four month flying course four years ago.
He was present at the private graduation ceremony during which William received his wings from Prince Charles at RAF Cranwell in Lincolnshire.
James, who served in Iraq and Afghanistan, died on March 16 when his bike was involved in a collision with a truck in Oxfordshire. A military funeral was held last month.
A spokesman for William said on Tuesday: "The Duke of Cambridge has been informed of the sad news and his thoughts are with Mr Hassell's family."