Image copyright Getty Images Image caption Both Gigi Hadid (L) and Katy Perry may have fallen foul of the Chinese authorities

A Victoria's Secret lingerie show is a glitzy affair. But some of the sheen was missing from its Chinese premiere on Monday, when most of the coverage focused on the two star names who didn't make it to Shanghai.

Reports say Katy Perry and Gigi Hadid's requests for visas were denied.

The response online in China has ranged from disappointment to schadenfreude.

The annual lingerie show is one of fashion's biggest events, attracting some 800 million viewers around the globe.

What happened?

The list of musical guests is usually kept under wraps, but it was rumoured that pop star Katy Perry would headline this year's fashion extravaganza.

Then the New York Post newspaper, quoting anonymous sources, reported that she had been barred from entering China "indefinitely".

Fashion model Gigi Hadid was also expected to walk the runway for Victoria's Secret, but she announced last Friday that she would not be able to go to Shanghai.

What's been said?

All we know about the reason for Hadid's no-show is what she said on Twitter.

As for Katy Perry, Victoria's Secret and Direct Management Group, which represents the singer, have not responded to the BBC's requests for comments.

Image copyright AFP Image caption These models did get their visas

And the Chinese government has not confirmed why - or even whether - the two were denied entry. It is unlikely to do so.

But the Global Times, a state-run tabloid, chimed in, saying that if it was true "they had brought it on themselves".

Did the stars step out of line?

So what did Katy and Gigi do to get themselves banned in China?

According to the New York Post, the musician was banned because she wore a sunflower dress when she gave a concert in Taiwan, which China considers a breakaway province, two years ago.

Sunflowers became an anti-China symbol on the island after the Sunflower Movement began in 2014.

Student protesters against trade deals with China occupied parliament for 24 days. They called for supporters to buy and send sunflowers to show solidarity.

On top of the sunflower dress, Perry also draped Taiwan's flag at the concert. It caused a backlash in China, with many accusing her of supporting Taiwanese independence.

For her part, Hadid was criticised as racist by Chinese netizens after her sister uploaded an Instagram video in which Hadid narrowed her eyes in an apparent attempt to mimic the Buddha shape of a cookie she was holding up to the camera. Many people were offended.

The supermodel apologised in September.

"It hurts me to hurt anyone," she wrote under a verified account on Weibo, the Chinese equivalent of Twitter.

"I want you all to know that it was never my intent to offend anyone through my actions and I sincerely apologise to those who were hurt or felt let down by me.

"I have the utmost respect and love for the people of China and cherish the incredible memories I have made while visiting in the past."

All the same many netizens were happy about Hadid's failure to enter China.

"She should never come to China to make money," said one Weibo user, Xiaoyujia-chen.

How popular is Katy Perry in China?

It's hard to quantify how many fans she has in China but her Weibo account has more than a million followers - not a huge number compared with Chinese celebrities.

Chinese fans call her "Fruit Sister" because of her colourful, fruit-themed costumes.

Image copyright Getty Images Image caption A strawberry, perhaps? "Fruit Sister" performed in this bright red outfit earlier this month

Last year, she was scheduled to perform for Alibaba's Singles' Day concert but she cancelled at the last minute because of a "family emergency", leaving a lot of her Chinese fans disappointed.

"Oh… sad. It doesn't matter and I wish I could see you next time," wrote Weibo user Mrs_Otoole.

Do celebrities often get stopped at the Chinese border?

Gigi Hadid and Katy Perry are not the only Western celebrities who have encountered problems entering China - usually because of politics.

Pop rock band Maroon 5's Shanghai concert was cancelled two years ago. The reason is unclear, but many guessed it was because guitarist Jesse Carmichael had tweeted to the Dalai Lama on the Tibetan spiritual leader's birthday.

They are particularly sensitive to celebrities' contact with the Dalai Lama - Lady Gaga and Bon Jovi have suffered backlashes for this before.

China anger at Lady Gaga-Dalai Lama talk

And in July, the Chinese government confirmed that Canadian singer Justin Bieber had been banned in China because of his "bad behaviour".

In 2014, Bieber posted a photo of himself visiting the Yasukuni Shrine in Japan, angering many in China.

Qin Gang, then spokesman of China's foreign ministry, said Bieber should learn more about the history of Japanese militarism.

Additional reporting by Yashan Zhao