'Sandra, I feel sick,' he said to her in church, before neatly vomiting into his top hat, which he passed to his ADC.
Unlike Philip, who loved Gordonstoun, Alexandra hated the girl's boarding school she was sent to, Heathfield.
There were several attempts at reconciliation, but in October 1953 Peter sued for divorce in Paris on the grounds of desertion.
Alexandra's childhood and adolescence followed the same rootless pattern of other exiled European royal families.
She and her mother drifted from Italy to London, before settling in Paris in 1935 at the Hotel Crillon.
Until March 1941 his uncle Prince Paul acted as Regent, but when his government - under the threat of Nazi invasion - ended Yugoslav neutrality by signing the anti- Comintern pact, he was overthrown in a coup and Peter declared of age.
On 6 April an enraged Hitler attacked Yugoslavia and Peter was flown to Greece, then to London.
Peter never recovered from what he saw as a betrayal, and the rest of his life was a relentless decline.
The Communists had seized virtually all the immense fortune of the Yugoslav royal family, and Peter was reduced to selling Alexandra's jewels to make ends meet.
Alexandra's mother thought her daughter was too young, and was relieved when King George II of Greece refused permission for the match.
Alexandra encountered further parental resistance when she and King Peter decided to marry in wartime London - this time from Peter's mother, Queen Marie of Yugoslavia.
A doctor arrived in time and the divorce petition was rejected; but the marriage never recovered.