They say it is not over until the fat lady sings – now it turns out that it is not even over when the diva breaks a leg. There cannot be a professional performer treading the boards with a better story about how they stuck to the rule that the show must go on than self-styled 'Yankee diva' Joyce DiDonato, who will be appearing on stage tonight at the Royal Opera House in a new production of Rossini's opera Il barbiere di Siviglia (The Barber of Seville).

It will not escape the attention of anyone in the audience that this will be – so far as is known – the first time a professional opera singer has performed the part of Rosina from a wheelchair.

They will also notice her leg is encased in plaster following an accident in front of last Saturday's audience in Covent Garden. DiDonato had just completed the solo "Una voce poco fa" early in Act 1. She walked to the edge of the stage and slipped, fell, and broke her calf bone.

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But instead of giving way to the pain, she hauled herself up and carried on performing. Her limp told the audience something was wrong, particularly when she next came on stage, with a walking stick. In the interval, an official of the Royal Opera House announced she had sprained her ankle, but would continue anyway.

By the time she was whisked to hospital, after the final bow, she had been standing on her broken leg for nearly three hours to the horror of medical staff. Time will tell whether there has been any permanent damage.

After four hours in accident and emergency, she felt strong enough to joke about it on her blog: "From here on out, I declare that no one (please!) ever ever ever wish me again, in the American fashion (despite it being Independence Day), to BREAK A LEG.

"I understand the good intention, but from here on out, wish me 'in the mouth of the wolf' instead, ok? That's far less likely to actually happen – although with my luck, you never know!"

She was not the only one who roused the audience's admiration that evening. Act 2 of Il barbiere includes a notoriously difficult aria, "Cessa di più resistere", which is often left out. The tenor, Juan Diego Flórez, playing Figaro, not only performed it like a virtuoso, but did so holding on to DiDonato to relieve the pressure on her throbbing leg.

"So far as I am aware, Rosina has never been performed in a wheelchair before," a spokeswoman for the Royal Opera House said yesterday. "There has probably been a wheelchair on stage as one of the props, but not with a leading member of the cast in it."

On her blog, DiDonato defended the unusual innovation of a wheelchair-bound Rosina. "There is no RULE that says Rosina might not have been suffering from a broken ankle, right? It could happen!!," she wrote.

She went on: "I have to send out an INCREDIBLE debt of gratitude to my wonderful cast mates (ha – CAST mates!), as well as to the amazing staff of the Royal Opera House who took amazing care of me, and then to simply salute one of the very finest operatic experiences I have ever been a part of.

"Señor Florez sang an unbelievable 'Cessa di più resistere' all the while being sure to help keep me on my feet."

Aficionados will also know that Rosina is asked by one of the minor characters what is the matter, and replies, "E' un granchio al piede", a colloquial way of saying "I've got cramp in my foot." You can bet she delivered that line with feeling.