The Queen’s younger sister finally bowed to constitutional pressure and publicly broke off her engagement to divorcee Group Captain Peter Townsend on this day in 1955.

Princess Margaret was a teenager when she first met the dashing Townsend – a married man 12 years her senior.

An RAF fighter pilot who had distinguished himself in the Battle of Britain, Townsend joined the royal service in 1944. Following the death of King George VI in 1952, he was made Comptroller of the Queen Mother’s household at Clarence House – becoming equerry to both her and Princess Margaret, who was then aged 22.

Group Captain Townsend divorced his wife in November 1952, his relationship with Princess Margaret blossomed, and the two planned to marry.  But in 1953, following the death of Queen Mary – and with her own coronation about to take place – Princess Elizabeth asked Margaret if she could wait a year before making their relationship public.

Townsend and Princess Margaret on a tour to South Africa in 1953.

But it was not to be. After newspaper photographs showed the Princess and Group Captain laughing and smiling at each other at the Queen’s coronation – with one reporter noting the way Margaret affectionately brushed a piece of fluff from his jacket – their relationship immediately became a source of gossip and headlines.

Under the Royal Marriages Act of 1772, Princess Margaret was unable to marry without the Queen’s consent before she was 25. The Queen, however, was the Supreme Governor the Church of England – and since 1936, the Church had refused to countenance the remarriage of divorcees.

The Queen transferred Townsend to her own household in an attempt to dissuade the couple from continuing their union. Prime Minister Winston Churchill took it further, effectively exiling Townsend by posting him to Brussels as an attaché to the British Embassy for two years.

[Read more: July 29, 1981 - Prince Charles marries Lady Diana in front of record global audience of 750 million]

Over that time, there appeared to be popular support for Princess Margaret – and in August 1955, when she turned 25, she no longer required the Queen’s consent to marry. She did, however, need the approval of Parliament – and the Government, led by new Prime Minister Anthony Eden, still refused to give this. On October 23, 1955, Margaret was told that if she proceeded with the marriage, a Bill of Renunciation would be placed before Parliament, stripping her of all rights and privileges.

The Princess and Group Captain mutually decided that the sacrifice was too great. "We had reached the end of the road," Townsend later wrote. "Our feelings for one another were unchanged but they had incurred for us a burden so great that we decided, together, to lay it down."

On October 31, 1955, Princess Margaret issued her historic statement, which was broadcast by the BBC.

“I would like it to be known that I have decided not to marry Group Captain Peter Townsend. I have been aware that, subject to my renouncing my rights of succession, it might have been possible for me to contract a civil marriage.

“But mindful of the Church's teachings that Christian marriage is indissoluble, and conscious of my duty to the Commonwealth, I have resolved to put these considerations before others.

“I have reached this decision entirely alone, and in doing so I have been strengthened by the unfailing support and devotion of Group Captain Townsend.”