A Polish woman, who was known as Anna Anderson, and who spent nearly all her adult life in mental hospitals and asserted her royal lineage to the Romanovs until her last breath, was the most famous impostor of Anastasia.

In 1967, British choreographer Kenneth MacMillan created a one-act ballet, “Anastasia,” for the Deutsche Oper Ballet, a West Berlin-based company of which he was then artistic director. A gripping psychological thriller—and a star vehicle for the legendary Lynn Seymour—the ballet centered on the troubled and traumatized world of Anderson, a delusional woman caught up in an identity crisis. Or was she a pawn of conspiracy and calculate deceit? (At the time of the ballet’s creation there was still a remote possibility that Anderson’s story could be true. However, the DNA tests, conducted ten years after Anderson’s death, in 1984, invalidated her royal claim once and for all.)

In 1971, just one year after having assumed the post of artistic director the Royal Ballet in London, MacMillan decided to expand “Anastasia” to a full-evening production by adding two more acts to precede the existing one, also with Seymour in the title role.

Describing the 1967 one-act “Anastasia,” the eminent British dance critic, Clement Crisp, wrote: “This production was a triumph of expressive dance, a triumph for Seymour.”

After the premiere of the 1971 full version of the ballet, however, many European critics were far less enthusiastic.

“The two added acts . . . are of a conventional classical style and of a realism which, without being socialist, would make the joy of the Bolshoi. Certainly there are several borscht recipes, but this one is difficult to swallow,” a reviewer quipped in the French newspaper Le Monde. A number of London’s critics were even more disapproving, viciously ridiculing both the production and the choreographer. (Following the ballet’s hostile reception, MacMillan, reportedly, suffered a mental breakdown.)

Arlene Croce, writing in the New Yorker about “Anastasia,” which was part of the Royal Ballet season at the Met, in 1974, was more generous in her opinion: “I didn’t find it nearly as awful as the word from London had led me to expect.“ She praised the originality of the ballet’s concept, pointing out that in “Anastasia,” MacMillan produced “a personal fantasy about a global cataclysm entirely from nothing.”

After nearly 50 years since its creation, “Anastasia” still remains in the repertory of the Royal Ballet. In 2016, the company brought it back on the stage of the Royal Opera House, after more than a 10-year hiatus, as a showcase for the Russian-born Bolshoi-trained Natalia Osipova, who made her debut in the title role.

The 2016 recording of “Anastasia” with Osipova’s performance was streamed by the company in May as part of ROH’s #OurHouseToYourHouse series.

“Anastasia” opens with a stark image: a lone woman (Anna Anderson) dressed in a hospital gown, facing away from the audience, watches a film clip of the Romanov family on a big screen. The camera zooms in on the face of Anastasia projected on the screen as the woman walks away from the darkening stage only to return, moments later, as the young Grand Duchess herself. Now she is Anastasia and the year is 1913.

The first act of the ballet takes place on the Imperial yacht. The Romanovs, clad in summer white, are having a great time, enjoying the sun and the breeze and the entertainment by the naval officers, who dance in their smart-looking uniforms and, later, inexplicably, in their bathing suits.

It all looks lovely and family-like, except nothing of substance is happening onstage. There is no plot or character development. And there is no suspense. The most dramatic moment of the proceedings, which surely interrupts the atmosphere of gaiety and fun, is when the hemophiliac Alexei, Anastasia’s younger brother, slips and falls, sending everyone on the yacht into a deep state of horror and concern. But the monk Rasputin saves the day as he picks up the little boy and performs his woody-magic tricks thus returning the young Tsarevich to health.

The first act ends on the ominous note, though: a telegram arrives with the news of imminent war. The Tsar and the Tsarina express their fears and concerns in a melancholic pas de deux; and the jovial naval officers depart only to reappear again, all dressed in combat attire and ready for a battlefield.

Act II takes place four years later, in 1917. The Romanovs are giving a state ball to celebrate Anastasia’s social debut. The royal palace is filled with festive aristocracy and high-ranked military contingent; and everyone dances, including Anastasia and her escort, a dashing young officer (Edward Watson). Alas, the dancing, even if elaborate and intricate in style and form, seems to go forever and take us nowhere; and just like in Act I, the dramatic potency of the second act is very low.

There is a brief spark of intrigue and theatricality in the scene, when the celebrated Russian ballerina, Mathilde Kschessinska (danced with flair and glamour by Marianel Nuñez), arrives and performs, with her anonymous partner, an exhibition duet. It’s not a secret (at least not for the Tsarina), that Kschessinska was a lover of Nicholas; and there is an engaging exchange of knowing glances and gestures among the participants of the love triangle. At one point, the visibly excited Tsar turns to Tsarina, gesturing toward the dancing Kschessinska with a wave of approval: “Isn’t she lovely?” The grim-faced Alexandra looks away and you can only imagine a train of thoughts rushing though her mind. The trio later expands into a quartet to include the menacing-looking Rasputin (Thiago Soares), who, in turn, was considered by many to be a paramour of the Tsarina herself.

The royal festivities—and the second act—end in a blood bath. The Bolsheviks storm the palace, bringing total devastation to the place and its inhabitants. (The massacre—and the prancing of the revolutionary comrades that preceded it—is accompanied by the so-familiar melodies of Tchaikovsky to which George Balanchine famously choreographed his “Diamonds.” This scene was particularly hard to watch.)

For all her youthful exuberance and vigor, Natalia Osipova as Anastasia has very little material (both choreographic and dramatic) to work with. In Act I, she effectively enters onstage on her roller skates, wearing a long white lacy dress and a wide-brimmed hat decorated with ribbons. She is a picture of youth and happiness and care-free life. Yet, as I was watching her performance in the first two acts, I couldn’t help thinking that Osipova, despite all the visible jollity she was trying to project, looked utterly uncomfortable in her role. Her smile was awkwardly unnatural; and her interactions with her older sisters and her parents looked oddly tense. Yet her dancing was lovely and proficient, even if the choreography for her heroine looked dramatically inept and dull.

In Act III, which takes place in a dark room of a mental hospital, everything changes – the choreography, the music, the atmosphere and the dramatic quotient and impact of the ballet itself. This is MacMillan at his most theatrical and thrilling. And as the delusional Anna Anderson, Osipova revels in the role’s ample dramatic possibilities; and her performance here is quite extraordinary.

When the curtain opens, she is seated on her bed, motionless, looking dazed and incoherent as if overpowered by the menacing nature of her hallucinations, as if the devastating dreams—the painful memories of her past—become more real for her than the reality. She is surrounded by nasty-looking nurses and a noisy clique of stylishly dressed ladies in big hats (relatives of the Romanov family, who reject Anna outright.)

As Anna, Osipova’s appearance is starkly different from the previous acts. No longer elegant, perfumed and sophisticated, no longer a lively young princess, she is altered and aged beyond recognition; deep lines surround her vacant eyes; her mouth is unsmiling. What we see is a face hardened by suffering and anguish—haggard, colorless and weary.

In a state of anxiety and dread, she nervously paces her room, her movements broken, spasmodic and flat-footed. She exudes helplessness and terror. Dressed in depressing grey, her shoulders hunched, she looks like a prisoner without hope for parole.

In Act III, Anna’s presumed story is told as an anguished dance in a series of flashbacks, beginning with her family’s brutal murder by a firing squad and her subsequent rescue by peasants, one of whom she marries. A vampire-like figure of Rasputin is a frequent visitor of her inflamed mind as Anna attempts “to recall” her royal past and to reclaim her identity. These flashbacks are violent, horrific and masterly realized.

If in the first two acts of the ballet, MacMillan uses Tchaikovsky’s Symphonies No. 1 and 3, respectively; in Act III, he sets the story to the haunting shimmers of Bohuslav Martinů’s Symphony No. 6 (Fantaisies Symphoniques), which provide a potent underpinning of “Anastasia’s” dramatic finale—and MacMillan’s remarkable evocation of the confused and tormented mind. Anna Anderson’s story was an elaborate fake, but there was not a single inauthentic note in Natalia Osipova’s brilliant portrayal of a troubled soul hopelessly entangled in a trap of memories and illusions.