Once upon a time, there was an 11-year-old Hungarian girl, with blond curls and big dark eyes and a beautiful singing voice and a singer mother who taught her how to use it. She was discovered, as such girls often are, and toured as a child prodigy; and she had staying power, which such girls often do not. At 17 she landed a role in a hit show written by one of the biggest names in show business. A great opera conductor tried to secure her services, but so did the film studios, and she became a movie star — all the more starry after falling in love with her handsome leading man. They married; made films together; starred together on Broadway; were known as the Love Couple all over Europe. They had two children. They lived happily ever after.

Their castle is still there. On the grounds of a country club north of New York City, the stone house stands like a fortress of memory. Walk through the iron gate and up the steps and into the long living room, filled with chairs set at conversational, slightly informal angles, as if a party had recently been given there, among the tables laden with framed black-and-white photos. And there she is: the same delicate figure, the same big eyes, the same fluting, melodious voice. Sharply dressed in an elegant knit jacket, she makes her entrance. Her name is Marta Eggerth, she has lived in this house since 1958, and she is turning 100 years old on Tuesday.

You might not know her name: because we on this side of the pond are not well versed in Central European operetta, or because you’re too young and don’t remember her in a couple of Judy Garland films, including “For Me and My Gal,” that she made after she was signed by MGM and came to Hollywood to make her fortune. (That part didn’t quite pan out, not least because her big number in “For Me and My Gal” ended up on the cutting-room floor; the studio didn’t want to risk having their rising star Garland overshadowed.) If you’re an opera fan, you know the name of her husband, Jan Kiepura, the Polish tenor, who foreshadowed the Three Tenors with his voice, his charm, and his willingness to reach out to audiences in more popular forms, outside the temple of opera.

Most of her films are so heavily colored by the popular tastes of their time that they are largely forgotten: movies with titles such as the 1930s’ “The Blue From the Sky” or “My Heart Calls You,” light concoctions layered with sweet songs like a Viennese cake. (“A tinkling score, a diverting script, and a cast with a pleasant sense of farce,” said the New York Times of “The World’s in Love” in 1937, made with another tenor, Leo Slezak.) Eggerth doesn’t expect you to have heard of them. She doesn’t care much about them herself. At the time she made them, she was working too hard, subject to the grueling schedule of filming the same movie in two or three languages in the days before subtitles. And today, “I live in the present,” she says. If she wants to hear herself sing, she vocalizes.

Yes, she vocalizes, with a sound that’s retained its silvery freshness. And she occasionally performs. Since 2005, she’s given a number of one-woman shows at New York’s Cafe Sabarsky, a replica of a Viennese cafe that hosts an upscale series of unconventional cabaret evenings. The bookers knew they had a promising idea, since Eggerth is a great storyteller and a stage animal, but they were slightly nervous about booking a 95-year-old woman. Would she, they asked her son Marjan before her first appearance, be able to perform for as long as 45 minutes? Marjan, a pianist who has helped tend his mother’s career in recent years and worked with her to release a two-CD set of her singing on his own label, said he thought she could. In fact, she couldn’t. Forty-five minutes was too short. She gave them an hour and a half.

She’s certainly got great stories. She seems to have met half the entertainers of the 20th century, from Vladimir Horowitz (who pronounced the upright piano in her dining room “not bad”) to Marian Anderson (with whom she appeared onstage in Budapest as a child) to the leading composers of 20th-century operetta, who wrote for her: Emmerich Kalman, Franz Lehar, Oscar Straus, Robert Stolz. At 17, she had the classic break of going on as the understudy for an indisposed star in Kalman’s “The Violet of Montmartre.” After that, the great conductor Clemens Kraus offered her a contract at the Vienna State Opera — on the condition that she take five years off and study Mozart. “I venerate Mozart,” Eggerth says today, eyes raised heavenward. “But I need something else, more passion when I sing; I am not a Mozart singer.” Instead, it was Lehar’s “Merry Widow” that eventually became a calling card with Kiepura, in Chicago, in Europe, and on Broadway for a few hundred performances in the 1940s. The choreography was by George Balanchine; the book, by a young writer named Sidney Sheldon, decades away from writing novels of his own.

That Eggerth didn’t successfully transition to Hollywood was in part bad luck. Universal Pictures signed her in the mid-1930s and offered her a screenplay by Preston Sturges that she says was “wonderful” — just before cost overruns on the movie version of “Show Boat” forced the company into foreclosure. She was picked up by MGM, where she asked herself, “Why are they giving me checks to do nothing?” She was especially restless since her dashing husband was on the other side of the country, singing at the Metropolitan Opera. Finally, she was offered a role — but her excitement ebbed when she read it. “What — this little thing?” she says. “I thought I was going to be [Kalman’s] Countess Maritza!” The role was a minor one in the Judy Garland film “Presenting Lily Mars,” and after “For Me and My Gal,” Eggerth got herself released from her studio contract and went off to supervise her husband. The Sturges screenplay? Torn up. “I did not want to risk that anybody would see it and perhaps copy.”

Her real-life romance, however, had many of the earmarks of one of Sturges’s screwball 1930s romantic comedies. Having worshiped Kiepura from afar when she first heard him when she was 14 — he was 10 years older — she found a kind of mutual antipathy when they actually met on the set of “My Heart Calls You” in 1934. Still, she couldn’t help noticing that when he was filming a romantic scene for the movie’s French version, he used mouth spray after kissing the French actress Danielle Darrieux. “He did not do that with me,” Eggerth says smugly. Within a couple of years they were married. And after a career of making films and touring together in operetta and even opera, Eggerth was devastated when Kiepura died suddenly of a heart attack in 1966. She vowed she wouldn’t sing again — until her mother, the steadfast fixture in her life, persuaded her to think about going back.

“My life was very boring,” she now says, disingenuously. “I did not go to parties. I did not drink. I had always to think about my voice.”

And she is still guarding it, carefully, at 100 years old, bemused at having survived so long with all her faculties intact.

“People ask me, How is it to be 100?” she says. “I say, I don’t know. I have no standard of comparison. You must ask me when I am 200 what it was like to be 100, and then I will be able to tell you.”