Both ex-soldiers had their relationship smeared when John thought James had a fling with his wife. The painful love triangle or the thought of it led John Watson (now a private guard) to the Army barracks near Windsor Castle on Wednesday.
The attacker grabbed old pal Trooper James Dicks, 28, who he thought was with his ex-wife at the location, tied him up with ropes and bundled him into a car boot.
James stayed bound in the boot of the car until he was dragged out by his angry friend. In a moment of distraction, the victim fought back but sustained stab wounds in the hand. He also got a slash on the head amid screams for help.
An off-duty police officer who happened to be near the location saw the alleged incident and raised the alarm.
James Dicks and John Watson served together in Prince Harry’s old unit called the Blues and Royals which is also part of the Household Cavalry.
Its ceremonial duties include guarding the Queen and it is based at Windsor’s Combermere Barracks.
Dicks is still in the unit but Watson is now with the Military Provost Guard Service, which protects Army bases.
It is believed Dicks is now in a relationship with Watson’s ex-wife Lynsey Foston.
He was said to have been taken to hospital for treatment but released later the same day.