MacMillan had been longing to create his own Romeo and Juliet after seeing John Cranko’s version for the Stuttgart Ballet. Lynn Seymour had danced Cranko’s Juliet as a guest artist in Stuttgart in April 1964; MacMillan had subsequently choreographed the balcony scene pas de deux for her and Christopher Gable to perform on Canadian television during their summer break that year.

Frederick Ashton, then artistic director of the Royal Ballet, gave MacMillan the green light for the complete ballet in September 1964. The company wanted a big new three-act ballet based on the play by Shakespeare, whose 400th anniversary was celebrated in 1964. Ashton had chosen not to mount the Romeo and Juliet he had made for the Royal Danish Ballet in 1955, fearing it would suffer by comparison with the large-scale Lavrovsky production the Bolshoi Ballet had brought to the Royal Opera House. MacMillan therefore had less than five months to create his first three-act ballet, which the company hoped to include in its 1965 American tour.

He, Seymour and Gable endlessly discussed their ideas about the characters as MacMillan choreographed the key pas de deux in each act – his starting point around which the rest of the ballet would be built. He and Seymour envisaged Juliet as a headstrong, passionate girl who makes all the crucial decisions: the secret marriage, in defiance of her parents’ wishes; taking Friar Lawrence’s potion; joining Romeo in death. Gable’s Romeo was a young man swept off his feet by love, dancing in dizzy exultation.

Romeo and his close friends, Mercutio and Benvolio, were given bravura steps that distinguished them from the street fighters in Verona’s market place and the stately aristocrats in the ballroom scene. MacMillan had hitherto avoided virtuoso steps because he thought them too conventionally balletic. Only Juliet and her girlfriends are on pointe: their choreography is contrasted with character dances and verismo crowd scenes. MacMillan broke the ballet conventions of the time by having the dancing evolve from naturalistic action. Unlike Cranko’s production, there are no picturesque poses for applause at the end of set-pieces. Unlike the Bolshoi production there are no spotlit entrances for the leading characters: Romeo is discovered in semi-darkness at the start of the ballet as Rosaline’s anonymous suitor; Juliet’s arrival at the ball in her honour goes unnoticed at first.

MacMillan wanted to show the lovers as youngsters at the mercy of a powerful patriarchal society. Georgiadis’s monumental designs – unusual, then, for a ballet – emphasised the oppressive might of Juliet’s surroundings. She is a small, vulnerable figure within the imposing Capulet household and, finally, laid out in the family vault. Even Friar Lawrence is to be found in a well-appointed monastery rather than a simple cell. Georgiadis and MacMillan took their inspiration from Italian Quottrocento paintings and architecture, as well as from Shakespeare. Franco Zeffirelli’s 1960 production of Romeo and Juliet for the Old Vic had been another influence, with its fortress of a palazzo guarding the Capulet family’s treasures – including their nubile daughter.

MacMillan borrowed from Cranko the harlots who animate the market-place scenes. It is they who get the action going in the first scene, as they roister with the three young bloods, Romeo, Mercutio and Benvolio, and provoke the indignation of the townspeople. Tybalt, one of the Capulet clan, provokes a fight with the Montague faction which develops into a lethal brawl. The Prince of Verona enters to put a stop to the fighting, commanding the warring factions to lay down their swords.

The second scene introduces Juliet, playing childishly with her nurse. Her parents enter with Paris, her intended bridegroom. When they leave, the nurse tells her gently that her girlhood is over.

The Capulets are giving a ball to mark Juliet’s entry into Veronese society. Romeo and his two friends decide to crash it, wearing masks as a disguise. During the formal dances, Juliet and Romeo fall in love before she realises that he is a Montague, a family enemy. When his identity is revealed, Lord Capulet intervenes to prevent Tybalt breaking the laws of hospitality by starting a fight.

After the ball, Juliet is on her balcony, dreaming of Romeo, when he enters below. She runs to join him in an ecstatic pas de deux expressing their love for each other.

In Act II, Romeo is a changed man in the market place, no longer at ease with his companions and the harlots. A wedding procession passes through, with acrobats entertaining the crowd to the sound of mandolins. The nurse arrives, bringing a letter for Romeo from Juliet, proposing a secret wedding.

Friar Lawrence marries the lovers, with Juliet’s nurse the only witness. Before the marriage can be consummated, Romeo is embroiled in a duel with Tybalt in the market place. Because Romeo had initially refused to quarrel with Tybalt, Mercutio had stepped in for a dare-devil sword fight, only to be stabbed in the back. Romeo avenges his dead friend, killing Tybalt in anger. He has to flee when Lady Capulet enters, overcome with grief, followed by her husband.

Act III opens in Juliet’s bedroom, the lovers asleep together. Romeo realises dawn is breaking and that he should leave. Juliet, frantic, tries to delay him, knowing he must go into exile. He departs just before Juliet’s parents arrive with Paris. Juliet rejects him, to her father’s rage, but she will be forced to marry him. In a dilemma about what to do, she sits on her bed, confounded, then rushes to seek Friar Lawrence’s help.

He gives her a potion that will send her into a death-like trance. Romeo is to be told of the plan so that he can rescue her from her tomb, in the hope that both warring families will then forgive them. (The audience has to learn this from the synposis or the play, along with the fact that Romeo fails to be informed of the plan.)

Juliet takes the potion and hides the phial under her pillow. When her parents return with Paris, she appears, reluctantly, to yield to their insistence that she must marry him that day. She makes herself swallow the bitter potion, and crawls in a daze back to her bed. Her bridesmaids come to prepare her for her wedding but find her apparently lifeless. Her nurse and parents are distraught with grief.

Juliet’s body is placed on a bier in the family crypt. Paris stays behind after the mourners leave. Romeo enters the vault to bid farewell to her, unaware that she is not in fact dead. He kills Paris, then lifts Juliet from the bier to embrace her for the last time in an excess of grief. He lays her limp body back on the stone slab and drinks poison he has brought with him. When Juliet awakes to find herself in the crypt, Romeo is newly dead. She finds the dagger with which he killed Paris and stabs herself, trying to reach Romeo’s body as she dies.

The curtain falls on the on the lifeless bodies without the reconciliation of the Montagues and Capulets with which Shakespeare ended his tragedy. The dual suicide has been painful, two young lives needlessly wasted.

Romeo and Juliet’s premiere, with Margot Fonteyn and Rudolf Nureyev in the leading roles, met with 43 curtain calls; the safety curtain had to be brought down to persuade the audience to leave the theatre. The critical response to the performers and the ballet was fulsome: ‘A spectacular asset to the repertoire . . . altogether a milestone for MacMillan’ (Observer); Kenneth MacMillan takes his place as one of the world’s leading choreographers’ (Daily Mail); Fonteyn’s Juliet was ‘all trust and purity, grace and gentleness, radiance and puppy love’ (Sunday Telegraph). Andrew Porter in The Financial Times was the first to reveal that the role of Juliet was not conceived in Fonteyn’s image: ‘Juliet is plainly a role conceived for Lynn Seymour, and so until we have seen her dance it we cannot be precise about MacMillan’s intentions’.

The first performances had gone to Fonteyn and Nureyev because they were a bigger draw than Seymour and Gable. The casting of the famous pair guaranteed a box-office sell out and massive publicity. Sol Hurok, the American impresario, had insisted that if the new ballet were to be included in the Royal Ballet’s next US tour, it must be associated with Nureyev and Fonteyn. Paul Czinner’s 1966 film of Romeo and Juliet featured Fonteyn and Nureyev for the same box-office reasons.

Seymour and Gable danced as the second cast, receiving adulatory reviews for their fresh approach to the roles. They were followed by three other pairings in the first London season and on the US tour in the spring of 1965.

MacMillan’s Romeo and Juliet soon became a signature work of the Royal Ballet’s repertoire, and the best known version of the Prokofiev ballet in Britain and the United States. During his lifetime, MacMillan mounted it for the Royal Swedish Ballet in 1971, American Ballet Theatre in 1985 and Birmingham Royal Ballet in 1992 (with new designs by Paul Andrews).