The ladies of the court, wearing long dresses and hats with trailing veils, moved in a stately minuet across the stage of the Coliseum Theater in London on Wednesday night, in the English National Ballet’s production of The Sleeping Beauty. They tapped their canes on the floor as the Prince looked on, circling elegantly with uniform poise and charm.

Nothing looked particularly unusual. But it was. One of those court ladies was a man: Chase Johnsey.

For the first time in modern ballet history, a male dancer is performing as part of the female ensemble at an international ballet company, signalling an important moment in an art form that often celebrates a particular ideal of femininity. Or, as the great choreographer George Balanchine said, “ballet is woman.”

But in a world with a heightened awareness of gender fluidity, and with transgender people increasingly accepted in a variety of professions, including acting and modelling, ballet is taking its own brave leap.

“I want to be seen as a ballerina,” said Johnsey, an American who identifies as gender fluid but uses male pronouns. “My hair is up, I wear makeup, female attire. I am able to do female roles and look the part, so that is artistically what I do.”

Tamara Rojo, the director of English National Ballet who offered Johnsey a short-term contract in March, said she was “very sensitive about this being seen as a publicity stunt.” Instead, she said: “This is about reflecting the world we live in. There are different races, cultures and beliefs in our company — this is another aspect of that view.”

But stringent physical norms still matter in ballet. It’s not like the theatre, which has embraced gender-switching with all-female accounts of Shakespeare, say, or Glenda Jackson playing King Lear. These may require some suspension of disbelief from the audience, but not a fundamental change in appearance or skill from the performer.

In ballet, though, the body is all. Female ballet dancers must conform, certainly in major companies, to specific aesthetic norms, which include thinness and ideas about harmonious proportions. (In modern and contemporary dance a far greater range of body types is accepted.)

And for the grand 19th century classical ballets like Swan Lake and The Sleeping Beauty — the backbone of the traditional repertory — the dancers in the female ensemble, known as the corps de ballet, must not differ too much from one another physically, since they embody collective groups of swans, sylphs or wilis (the spirits of jilted girls). Johnsey, 32, is dancing in the corps, and a corps dancer must blend into the group, not stand out from it.

There are also important technical differences between men and women in ballet. Men have bigger, more athletic jumps and turns, and they lift and carry the women. The female dancers perform on point — dancing on their toes in stiffened ballet shoes — a skill they begin to learn as teenagers and which requires a different strength and training from men’s.

Johnsey, who has had facial surgery to feminize his features, already had some of these skills before joining English National Ballet. In an interview a few days before the opening of Sleeping Beauty, he said he began to dance on point, secretly, as a teenager, after beginning ballet at 14. Three years later, he joined Les Ballets Trockadero de Monte Carlo, an all-male comedic troupe in New York whose dancers play both male and female roles.

The Trocks, as they are known, perform technically demanding ballerina roles on point, and Johnsey was acclaimed for his brilliance and delicacy in these roles. Last year, he won the best male dancer award at Britain’s National Dance Awards — mainly for his appearances with the Trocks.

(Johnsey left the Trocks at the start of the year, alleging he and other dancers were mistreated and harassed for appearing too feminine in classes and rehearsals. The company appointed an independent investigator, who did not substantiate these claims.)

But when Johnsey joined English National Ballet, he discovered that performing in drag with comic intent is very different from performing as part of a seamless female ensemble.

“With the Trocks, if you messed up, you could make a joke about it,” he said. And despite his strong point-work technique, he said he had “completely the wrong idea about what makes a ballerina beautiful and graceful. It is actually strength, hidden within softness and grace, and I have had to figure out in my genetically male composition, how to find that.”

Johnsey is not appearing on point in Sleeping Beauty but in what are known as character, or soft-shoe, dances, with costumes less revealing than those for point-work roles. His path even to these appearances has been arduous. Since beginning work at English National Ballet, he has lost 20 pounds, with the help of a nutritionist, and worked with both a physical trainer and a company ballet mistress, Loipa Araújo, to retrain and reshape his body.

“I am a small, petite guy, but I am a man,” Johnsey, who is 5 feet 5, said. “My shoulders are wider, my calves are bigger, the textures of my muscles are different.” He added, “I had to cannibalize my body, make it run on energy from muscles and figure out how to lose muscle mass without losing strength.”

The company dancers, Johnsey said, had been welcoming. “I have never felt like a freak here,” he said. “But I’m aware that not everyone will support me and that there will probably be a backlash.”

Isabelle Brouwers, a corps de ballet dancer who performs with Johnsey in the Mazurka in Act 3, said there had been no prejudice or hostility when he joined the company. “I think it’s a great and positive step in bringing ballet into the 21st century,” she said.

(Rojo could use some positive buzz; in January, The Times, citing unattributed sources, reported that English National Ballet had lost a third of its dancers in two years amid claims of verbal abuse, a hostile work environment and a conflict of interest in Rojo’s romantic relationship with Isaac Hernandez, a principal dancer.)

But while Johnsey’s appearance with a ballet company can be seen as a boost for gender equality, it could also be viewed as a man infiltrating an already competitive female domain. Wendy Whelan, the former New York City Ballet principal, said she had conflicting feelings.

“I don’t care what the body parts are, as long as artistically the dancer makes the choreography shine,” Whelan said. “If he is the best girl for the job, then great.” But, she added, this could be “another hurdle” for women in a field that is more difficult for them to succeed in than men. “Living the life of a woman in ballet means not having access to the privileges that come with the patriarchy,” she added.

And Isabella Boylston, a principal with American Ballet Theater, said that she didn’t see an issue “if they are open to it going both ways” and have women in male roles, too.

Jennifer Homans, who wrote Apollo’s Angels, a widely praised history of ballet, pointed out that female roles were performed by men at the earliest moments of ballet’s history at the court of Louis XIV. Although ballet is a very gender-specific and rigid art form in some ways, she said, “in other ways that’s not true. It has long been a platform for men to feel and express femininity.”

What matters, she said, was “not whether men dance as women and women as men, but whether the effect is artistically interesting.”

Will Johnsey’s small step — an unobtrusive appearance with the female corps in one of the most conventional of all ballets and companies — be a breakthrough for gender fluidity in ballet?

There are already signs of an opening up. In the last few years, there have been far more instances of choreographers creating same-sex duets, and being more unconventional in casting choices; recently, choreographer Justin Peck, at the New York City Ballet, put a woman in a role originally conceived for a man.

“I think ballet can be the perfect environment for gender fluidity,” Rojo said. “We are in a position where we could open up roles for lots of people. Obviously, certain roles require physical strength for lifting, and are less obvious for crossover. But the potential is there.”

Could Johnsey be a swan, a princess or a wili? “I don’t see why not,” she said.