The Duke of York fought in the conflict, which started in 1982 following Argentina's invasion of the British territory. The royal served as a helicopter co-pilot and was stationed on the HMS Invincible during the war. His duties in the war consisted of Exocet missile decoy, evacuating causalities and air and sea rescue, as well as engaging in anti-submarine and anti-surface warfare.
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Although Andrew and Sarah knew each other while he was serving, they weren't together at the time, with the royal being in a relationship with photographer and actress Koo Stark.
"I asked Andrew this morning for his reflections on the anniversary of his sailing from Portsmouth to the Falkland Islands 40 years ago," Sarah wrote at the beginning of a series of now-deleted posts where Andrew recalled his service.
In one part of his lengthy remarks, the Duke said: "I did get shot at, but it was not intended for me, at the time Atlantic Conveyor was hit, I was airborne in the anti-submarine screen and told to climb to height and drop chaff (to confuse the enemy radar into believing there were many more targets than they thought and make their targeting solution more difficult and then to confuse the missiles into choosing the wrong target).
"I was flying and saw a chaff shell fired from one of our ships that passed not that far in front of us. For a moment it was on a steady bearing before it began to cross to our left. The terror that that was going to be that, just for a moment, has had a lasting and permanent effect on me.
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"We then had to put that to one side and get on with the search and rescue mission to recover and find men in the water after Conveyor was hit and burning."
He then revealed that he had a "full weep" while processing his memories as he thought about the people of Ukraine following Russia's invasion of the country.
He reflected: "We can't seem to learn from our history of conflict that it is the human being that suffers, it is the families that are torn apart by the indiscriminate bombardments, it is the bravery and courage of the few to defend the many that has really caught me as I reflect."
The Duke served during the Falklands War
The final post was of the Duke during his time in the military and ended with him explaining how serving in war had changed him.
"So whilst I think back to a day when a young man went to war, full of bravado, I returned a changed man," he wrote.
"I put away childish things and false bravado and returned a man full in the knowledge of human frailty and suffering. My reflection makes me think even harder and pray even more fervently for those in conflict today, for those families torn apart by the horrors they have witnessed.
"And, I'm afraid to say, that the historical perspective my short war has taught me is this - war is failure to keep peace; war is failure of human judgement; war is failure to recognise we need to seek permission to understand another person's perspective or reality, whether or not we agree or disagree with that perspective or reality."
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