The line is spoken by Lady Bracknell, played by Nancye Hayes in the State Theatre Company of South Australia's production of the Oscar Wilde comedy. Many people have asked her how she is going to say THE line.

Hayes' career - which has encompassed singing, dancing, choreographing and directing as well as acting - began as an 18-year-old dancer in the original Australian production of My Fair Lady in 1960. But despite a long list of stage credits over the ensuing five decades, she had never appeared in The Importance of Being Earnest, Wilde's most popular play, which was first produced in 1895.

It's a comedy of manners set in Victorian England in which two young bachelor friends engage in deceptions. Jack invents a brother, Ernest, as an excuse to leave behind the dull life of the country and go to London so he can pursue Gwendolen, daughter of the formidable Lady Bracknell. Gwendolen is the cousin of the other bachelor, Algernon, who has invented a fictitious invalid friend in the country named Bunbury whom he can "visit" when he feels the need to get away from London. He is interested in Jack's young ward, Cecily. But the truth will out.

Director Geordie Brookman says, "Part of the reason Wilde’s beautifully ridiculous play remains an enduring challenge for artists and a delight for audiences is because he manages to aim all his satirical and absurdist powers at a core group of innate human flaws while retaining a unique warmth."

Hayes is very pleased to be cast as Lady Bracknell.

"It was one of the roles I hoped I might get in a career,'' she says.

She's seen many other interpretations of the formidable woman - Edith Evans in the 1952 film version, Ruth Cracknell, even Geoffrey Rush in drag - but says it is important to give it her own interpretation ("and that of the director").

As for that famous line, she says she will find her own way of doing it and jokes, "I feel like saying to the audience, 'All together now!'''

One of the challenges of the play, she says, is the language, with Wilde's very precise deployment of words. "It's difficult to learn - you're always making sure the right words are in the right place."

But that is also one of Earnest's charms. "It is particularly witty," Hayes says,

She also thinks a lot of the things said in the play are quite relevant today in terms of social manners and mores and attitudes to love and romance. But she's happy it is a very traditional production in terms of its settings, costumes and performance.

"I'm very grateful for that. Sometimes people like to update things, don't they? And it doesn't always sit that well."

Not that traditional means boring. She says this Earnest is a joyful production with lots of opportunities for physical as well as verbal humour.

Brookman says. “Divining the moments when to break the ever-present code of manners (who knew that doing that with your gloves meant that!) or cut across the extraordinary musicality of his text has been invigorating and made for a wonderful, silly rehearsal room.”

It's been a few years since Hayes was in Canberra with a show - the last time was in 2011 with Reg Livemore in Turns - but she's no stranger to the nation's capital. She came here a few years earlier in Opera Australia's production of My Fair Lady - as she notes, "I was one of the dancers in 1961 and 48 years later I was Mrs Higgins."

She remembers that musical well - "a beautiful show based on a classic" - that ran for about five years. She was with it for two, and stayed a dancer throughout: in those days, dancers, chorus and actors were separate with no crossover.

"It changed after that to an ensemble ... it changed with shows like West Side Story."

She got one break when she understudied then took over the role of Hedy LaRue in How to Succeed in Business Without Really Trying from the original American actress. It was common practice then for overseas performers to be imported for principal roles, even if they were not well known.

"They were often good performers but certainly not stars," Hayes says. Her experience signalled a change. "That was the beginning of Australian performers being cast in leading roles."

Now, of course, many Australians are working on Broadway and the West End and shows are routinely cast here with local talent - that particular brand of cultural cringe is over.

"We've gotten over that. We have a lot of people going over there."

Hayes appeared in several other shows including Hello, Dolly!, Kiss Me Kate and Brigadoon, but her big break came in 1967 when she was cast in the title role of Sweet Charity.

"It was my first really big lead - singing, dancing, acting ... a star vehicle role."

And she never looked back. Her musical theatre credits include Dames at Sea, Promises, Promises, Cabaret, Pippin, Sweeney Todd, Annie and 42nd Street. But she added other strings to her bow, moving into cabaret, non-musical plays, choreography and direction.

Although she had studied dance and singing, most of her learning was on the job - there were no institutions like the Western Australian Academy of Performing Arts when she was starting out so the J.C. Williamson theatre company was effectively her training ground.

Hayes remembers the first time she wore a mike - "they were like bricks" - in Chicago, in the early 1980s but says performers need to be aware not to rely on them: they have to project their own voices. But with bigger venues and amplified instruments, they're a necessity.

While Hayes has seen and done a lot and has many fond memories, she does not live in the past. She has appeared in recent shows like Grey Gardens, enjoyed seeing more recent musicals like Wicked and The Drowsy Chaperone and looks forward to seeing the recent Tony Award winner, A Gentleman's Guide to Love and Murder. She hopes someone will bring it out here.

Hayes has worked on Australian musicals such as Eureka but acknowledges that the only Australian-created shows to have made a big impact overseas have been jukebox shows like The Boy from Oz. She attributes this to the high cost of developing and mounting shows and the preference of producers to turn to shows with established success overseas. But, she says some people are still trying both to create new homegrown shows and to give them opportunities to be seen.

Hayes's career longevity and accolades - including, this year, becoming a Member of the Order of Australia - speak for themselves but she still takes nothing for granted. "I am very thankful to be able to continue working" she says.Her advice for young people pursuing a career in the theatre is simple: "Be ready".

It's a principle that has kept her working steadily for more than half a century, with no end in sight.

The Importance of Being Earnest. By Oscar Wilde. Directed by Geordie Brookman. State Theatre Company of South Australia. The Playhouse, Canberra Theatre Centre. August 19-23. Tickets $35-$65. Bookings: 6275 2700 or canberraticketing.com.au.