The Princess had reportedly accepted Armstrong-Jones' proposal a day after learning from Peter Townsend, to whom she had been romantically linked after the death of her father, that he intended to marry a young Belgian woman, Marie-Luce Jamagne.
The engagement was announced on 26 February 1960 and the couple posed for photographers at Windsor Castle. Princess Margaret received a ruby and diamond engagement ring that was designed by her future husband to look like a rosebud, in honour of the Princess' middle name, Rose.
The official statement from Clarence House announcing the engagement read:
It is with the greatest pleasure that Queen Elizabeth The Queen Mother announces the betrothal of her beloved daughter The Princess Margaret to Mr Anthony Charles Robert Armstrong-Jones, the son of Mr R.O.L. Armstrong-Jones QC, and the Countess of Rosse, to which union The Queen has gladly given her consent.
You can compare it to Princess Elizabeth's engagement announcement here.
The task of creating the wedding gown fall to royal couturier Norman Hartnell, a ballgown-style dress in white silk organza, high neckline, moulded bodice and flowing skirt, completely devoid of embellishments or embroidery. In 1960, Life magazine named it "the simplest royal wedding gown in history".
A silk tulle veil, ordered by Hartnell from Paris and made by Claude St Cyr, fell from the ornate Poltimore tiara, which the bride herself had bought at auction in 1959 for £5,000. Upon her death in 2002, it was auctioned again, together with other pieces in her collection, to help pay estate duties. This time, the tiara sold for £ 926,400, against a top estimate of £ 200,000.
The tiara sat upon a hairpiece selected by the bride's hairdresser René, to add height.
The Princess wore the tiara throughout her life and was famously photographed by her husband while wearing it in the bathtub:
The Princess wore the tiara throughout her life and was famously photographed by her husband while wearing it in the bathtub:
Princess Margaret's wedding shoes were made by royal shoemaker Edward Rayne in a court style, of white crepe faced with satin and with slender 2 1/2 inch heels.The bouquet included the traditional myrtle. The official photographer was Cecil Beaton.
The couple were married at Westminster Abbey. The Princess had chosen to travel to the Abbey in the Glass Coach, more often used to bring brides back to the Palace. Prince Philip gave the bride away.
It was the first real televised wedding, reaching three hundred million people worldwide, an extraordinary audience for the time. Guests included Winston Churchill, Noel Coward and John Betjeman.
It was the last time the Queen wore a floor-lenght dress to a daytime wedding (she wore a long dress to the wedding of her son Prince Edward to Sophie Rhys-Jones in 1999, but that was in the late afternoon), another Hartnell creation in sky blue silk with elaborate lace detailing, complete with the Lovers' Knot brooch (the same she wore fifty years later to the wedding of Prince William to Catherine Middleton).
After the wedding breakfast and the balcony appearance, the newlyweds departed in an open-topped Rolls-Royce to board the royal yacht Britannia at the start of a six-week Caribbean cruise. After their return, they moved into rooms at Kensington Palace.
Prince Charles (far left) and Princess Anne (centre right) helped send the newlyweds on their way: