A well-executed production featuring top opera singers ended on a sour note.

On Sunday, the audience at the Sejong Center for the Performing Arts in Seoul erupted in applause and cheers after tenor Kim Jae-hyung's powerful rendition of the iconic aria "E lucevan le stelle" (When the stars were brightly shining) in Puccini's "Tosca," produced by the Seoul Opera Company. Kim, also known as Alfred Kim, was onstage for his second performance as Cavaradossi, Tosca's lover, with renowned soprano Angela Gheorghiu, who has portrayed Floria Tosca numerous times during her illustrious career.

Kim, whom Gheorghiu had praised for his remarkable voice during a press conference on Aug. 30, reciprocated the applause and cheers by singing the aria one more time.

While opera audiences are divided over the appropriateness of encores during a performance, interrupting one with angry outbursts was unexpected.

As the audience settled back in to enjoy the encore, Gheorghiu suddenly appeared on stage with an angry expression, pacing about. She then abruptly addressed the audience, saying, "Excuse me," followed by, "This is not a recital. Respect me."

After Gheorghiu left the stage and Kim finished his song, the audience gave him a big round of applause, but the audience's experience of the performance had undeniably been affected. Despite the unsettling situation, Gheorghiu and Kim carried on with the next scene, and the performance concluded without further interruptions until the tragic ending of the opera.

However, the evening's drama was not quite over. Gheorghiu, who was supposed to be the last performer to take the stage and receive the spotlight during the curtain call, did not appear immediately. Even as Kim, Samuel Youn (who played Scarpia), and the rest of the cast, along with the audience, applauded and waited, she delayed her entrance. When she finally did come on stage, a few boos erupted from the audience, prompting her to angrily turn around and storm off the stage.

The rest of the cast appeared visibly flustered, while conductor Jee Joong-bae, director Pyo Hyun-jin and Park Hye-jin, head of the Seoul Opera Company, forced smiles as they greeted the audience.

Some audience members criticized Gheorghiu for what they called "disrespectful behavior toward the Korean audience," with a few even demanding refunds from the Sejong Center or requesting an official apology from Gheorghiu.

The Seoul Opera Company issued an apology on Sunday night, saying it is demanding an apology from Gheorghiu.

“Something unthinkable happened, pushing everyone into chaos. The production teams and cast put their utmost efforts into the production, but it’s unfortunate that the last performance was ruined like that,” an official at the Sejong Center for the Performing Arts told The Korea Herald.

The organizer stated that they are considering how to address the issue in addition to demanding an apology and are reviewing similar cases from the past, including one involving Gheorghiu.

In April 2016, during a performance of Tosca at the Vienna State Opera, Gheorghiu failed to appear after an encore of "E lucevan le stelle," performed by the renowned tenor Jonas Kaufmann. After a minute-long awkward silence, Kaufmann commented, “It seems we don’t have a soprano.” When Gheorghiu still did not appear, Kaufmann apologized to the audience, and after another pause, Gheorghiu eventually came on stage, allowing the performance to continue.

Meanwhile, the Seoul Opera Company's production of "Tosca" highlighted the talent of its other cast members. The opera featured two teams: one with Gheorghiu, Kim, and Youn, and the other with soprano Rim Sae-kyung, tenor Kim Young-woo and baritone Yang Jun-mo.

While Gheorghiu's celebrity status contributed to near-sold-out ticket sales for the production's first and fourth day performances, the Sejong Center saw an increase in ticket sales for Rim's team after its performance on Friday.