A suspected Chinese spy - described as a "close confidant" of Prince Andrew - has been publicly named as Yang Tengbo.
Mr Yang, who was known only as H6 until a High Court judge lifted an anonymity order which was shielding his identity on Monday, is barred from entering Britain.
He was first excluded in 2023 by then home secretary Suella Braverman after the Home Office said he was considered to have engaged in "covert and deceptive activity" on behalf of the Chinese Communist Party (CCP).
The case against Mr Yang has recently been thrust back into the limelight after he argued his exclusion from the UK was unlawful and made an appeal to the Special Immigration Appeals Commission (SIAC).
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Last week, the specialist tribunal in London upheld the ban and ruled that Ms Braverman had been "entitled to conclude" that he "represented a risk to the national security".
MPs have since expressed concern about the level of access allegedly gained by the businessman, after he also met former prime ministers Lord David Cameron and Baroness Theresa May.
Here is everything we know about Mr Yang so far.
Who is Yang Tengbo?
Mr Yang is a 50-year-old Chinese national who worked as a civil servant in China before coming to the UK as a student in 2002.
In Britain, he set up a consultancy firm called Hampton Group International - an advisory group that helped with relationships between the UK and China.
He is also credited as the co-founder of Pitch@Palace China - the Chinese branch of the Duke of York's scheme, which was set up to help support entrepreneurs.
Mr Yang is alleged to have been working on behalf of the CCP and United Front Work Department - an arm of the CCP which critics say is used to influence foreign entities.
Judges at the SIAC tribunal were told that in a briefing for the home secretary in July 2023, officials claimed Mr Yang had been in a position to generate relationships between prominent UK figures and senior Chinese officials "that could be leveraged for political interference purposes".
They also said that My Yang had downplayed his relationship with the Chinese state which, combined with his relationship with Andrew, represented a threat to national security.
The three SIAC judges said on 12 December that Mr Yang had enjoyed a private life in the UK, which had been described as the businessman's "second home".
They said he had "settled status, a home and extensive business interests in the United Kingdom. He was regarded as a close confidant of the duke".
Relationship with Prince Andrew
It is not known precisely when the duke and Mr Yang met, but a statement released by Andrew on Friday said the pair met through "official channels".
It is believed they grew so close that the businessman was invited to the royal's birthday party in 2020, visited Buckingham Palace twice, and also entered St James's Palace and Windsor Castle at the invitation of the duke, according to The Times.
Mr Yang was also told by Andrew's aide Dominic Hampshire that he could act on the duke's behalf when dealing with potential investors in China.
The SIAC tribunal heard that a March 2020 letter from Mr Hampshire - referencing the invitation to the duke's birthday - was found on Mr Yang's devices when he was stopped at a port in November 2021.
The adviser said in the letter: "I also hope that it is clear to you where you sit with my principal (Prince Andrew) and indeed his family.
"You should never underestimate the strength of that relationship... Outside of his closest internal confidants, you sit at the very top of a tree that many, many people would like to be on."
Judges who upheld the ban on Mr Yang entering the country argued the duke could have been made "vulnerable" by his influence.
The duke's statement said he "ceased all contact with the individual after concerns were raised".
"The duke met the individual through official channels, with nothing of a sensitive nature ever discussed. He is unable to comment further on matters relating to national security," the statement said.
Several newspapers have reported that the King has been briefed about his brother's links to the alleged spy.
Former Conservative Party leaders Lord Cameron and Baroness May were also pictured with Mr Yang.
There is no suggestion either of them were aware of his reported links to the Chinese state, and it is not known when the images were taken.
Both Lord Cameron and Baroness May's spokespeople told Sky News they meet and are photographed with many people each year.
Baroness May's spokeswoman said she does not remember "when or where the particular photograph was taken or the man in question".
While a source close to Lord Cameron said: "David Cameron was leader of the Conservative Party for over a decade and PM for six years.
"He met thousands of people in that time at hundreds of functions and events. We don't have any further information about this individual."
'I have done nothing wrong'
In a statement after his identity was revealed, Mr Yang said the allegations against him are "entirely untrue".
He said he is a victim of a "political climate" which had seen a rise in tensions between the UK and China.
"I have done nothing wrong or unlawful and the concerns raised by the Home Office against me are ill-founded," Mr Yang said, adding: "The widespread description of me as a 'spy' is entirely untrue."
He said he is seeking to appeal the decision of the SIAC.
Mr Yang continued to say that he is "an independent, self-made entrepreneur" who has "always aimed to foster partnerships and build bridges between East and West".
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He said: "I have dedicated my professional life in the UK to building links between British and Chinese businesses.
"My activities have played a part in bringing hundreds of millions of pounds of investment into the UK.
"I built my private life in the UK over two decades and love the country as my second home. I would never do anything to harm the interests of the UK."
What has China said?
A spokesperson for the UK's Chinese embassy said last week that some in the UK are "so keen" on making up "all kinds of spy stories against China".
"This again is a typical case of the thief crying 'catch thief'," they added.
"Their purpose is to smear China and sabotage normal people-to-people exchanges between China and the UK. We strongly condemn this."
They also said the United Front "endeavours to bring together various political parties and people from all walks of life, ethnic groups and organisations" to "promote cooperation between the CCP and people who are not members of it".
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"Some on the British side repeatedly use China's United Front work as a pretext to accuse China of wrongdoing, discredit China's political system, and undermine normal exchanges and co-operation between China and the UK.
"Such sinister plots will never succeed. We urge the relevant parties in the UK to immediately stop creating trouble, stop spreading the 'China threat' narrative and stop undermining normal exchanges between China and the UK."
(c) Sky News 2024: Who is Yang Tengbo? What we know about the Chinese 'spy' with links to Prince Andrew