PARIS — After the Chanel designer Karl Lagerfeld died last February at age 85, a rumor began to circulate: He had left his fortune, and a large part of his worldly goods, to his Birman cat, Choupette.

The estate hasn’t been settled yet, and Mr. Lagerfeld’s team remains mum on the subject. But the public’s concern for the desolate puss was genuine. “People came by the store and said how sad they were, and half of it was about Choupette,” Caroline Lebar, the longtime head of communications for the Karl Lagerfeld brand in Paris, recalled earlier this month. “They’d say, ‘If she’s alone, I’ll take her home.’ ”

Since then, fans have continued to inquire: How is Choupette? Where is Choupette?

“It’s like unlocking a mystery,” said Stephen Gan, editor of V Magazine. “What happened to Choupette?”

According to Ms. Lebar, “She lives with her nanny” — the former Lagerfeld housekeeper Françoise Caçote — “here in Paris. She is in good shape, and is surrounded by love.”

She is also very busy, said her agent, Lucas Bérullier, of My Pet Agency in Paris. “She comes to the agency on occasion, and we do photos here for her Instagram account,” which Mr. Bérullier and Ms. Caçote debuted on Choupette’s birthday last summer. “We have beautiful projects” celebrating Choupette.”

Choupette was born Aug. 15, 2011 — a Leo, like Coco Chanel. Her fur color has been compared to Baked Alaska, and Mr. Lagerfeld declared that her eyes were like star sapphires. She originally belonged to the French model and Lagerfeld friend Baptiste Giabiconi — he received the 10-week-old kitten as a birthday gift from friends who knew he loved Birmans. He named her Choupette, “a common nickname in French for cute girls,” he said in a recent interview.

That Christmas Mr. Giabiconi went to Marseille to see his mother and asked Mr. Lagerfeld to cat sit. At first, Mr. Lagerfeld was hesitant. The fur! But then he acquiesced —“‘since cats take of themselves,’” Mr. Giabiconi recalled the designer saying.

When Mr. Giabiconi returned, he brought Choupette home — and Mr. Lagerfeld went into a deep funk. “He was angry. He wouldn’t speak to me,” Mr. Giabiconi said. “After a week of reflection, it became clear to me that Choupette brought Karl great joy.”

Mr. Giabiconi went to Mr. Lagerfeld’s apartment on the quai Voltaire, and knocked on the door. When Mr. Lagerfeld opened it, Mr. Giabiconi handed over the kitten. “No one could give me a more beautiful gift,” he recalled Mr. Lagerfeld saying. “She has brought sunshine to my life.”

But Mr. Lagerfeld wanted to change her name. “He thought Choupette was ugly,” Mr. Giabiconi said. “I said, ‘That’s a mistake. Choupette works in every language.’ ‘Ah, yes, it’s true.’ And now it’s taken on a life of its own.”

Thanks to Mr. Gan. Following dinner together in Paris in January 2012, Mr. Lagerfeld invited Mr. Gan to his apartment to meet Choupette. “I thought, ‘What? Karl has a cat?’ He was the last person I thought would get a pet,” Mr. Gan said.

But sure enough, there was Choupette, sitting primly next to a bouquet of roses. Mr. Gan whipped out his phone, took a picture and posted it on V Magazine’s Twitter feed: “Meet Choupette.” It went viral.

Soon enough, there were Instagram accounts dedicated to Choupette; glossy magazine spreads featuring Choupette (usually photographed by Mr. Lagerfeld); a makeup line by Shu Uemura called Shu-pette; a novelty book titled “Choupette: The Private Life of a High-Flying Fashion Cat” ; and loads of other things. (In 2015 alone, she pulled in more than $3 million.) Chanel collections suddenly included a new shade dubbed “Choupette blue,” and the Karl Lagerfeld brand put out a range of Choupette face handbags.

As her fame grew, so did her entourage: She had two minders, including Ms. Caçote; a bodyguard; a doctor; and a chef. “Do you know Velázquez’s painting Las Meninas, with the Infanta Margarita surrounded by servants?” Mr. Lagerfeld once was quoted as saying by Harper’s Bazaar. “That’s Choupette.”

She traveled with Mr. Lagerfeld, preferably flying private; he designed a Louis Vuitton carrier bag for her, as well as a Goyard case for her silver dishes and brushes. Their last excursion was in December 2018 to New York for Chanel’s Métiers d’Art show at the Metropolitan Museum of Art. They lodged at The Mercer hotel in Soho, and received friends for drinks in the lobby.

“Choupette changed Karl’s life,” Amanda Harlech, Mr. Lagerfeld’s style consultant at Chanel, said. “He couldn’t believe how happy she made him nor how she loved being by his side — even sleeping on his head! He would watch her for hours.”

“She’s a very powerful young lady, Miss C.”

It’s not over, either. According to Mr. Bérullier, her agent, “She has press demands every day, and some deals en route.”

She also has her book: “Choupette,” a monograph published by the German house Steidl Verlag. The small hardback, bound in a morning blue linen that matches her eyes, is a collection of iPhone snaps by Mr. Lagerfeld of the fluffy feline at play and at rest. Mr. Lagerfeld designed and edited the book in 2018 to give to his friends as Christmas presents.

In January 2019, the head of Steidl Verlag, Gerhard Steidl, asked Mr. Lagerfeld if the house could reissue it commercially. “O.K.,” Mr. Steidl recalls Mr. Lagerfeld as responding. “But wait a little bit.”

Mr. Lagerfeld died of pancreatic cancer a few weeks later. Mr. Steidl released “Choupette” in November, and within weeks, it sold out. (He wouldn’t release sales figures, but said the house is awaiting delivery of the second printing). All royalties go directly Choupette.

“She is a business,” Mr. Steidl said. “She has a bank account.”