Sophie Wessex's disgraced PR business partner has resigned from the Institute of Public Relations after failing to explain his behaviour in the "Sophiegate" scandal.
Murray Harkin was exposed by an undercover News of the World reporter for offering to arrange sex parties for clients.
Mr Harkin declined to appear in front of the PR body to give his side of the story.
The IPR, of which Mr Harkin and the Countess of Wessex are members, launched an investigation into his behaviour amid fears he had brought the industry into disrepute.
The organisation wrote to Mr Harkin asking for his side of the story but he declined to appear in person to the IPR's professional practices committee or to provide a written comment.
An IPR spokeswoman said: "As he provided no information it has not been possible for the institute to establish the truth surrounding the matter.
"The institute felt it had no option but to accept Mr Harkin's resignation. The matter will remain on file and will be reopened if Mr Harkin were to reapply for membership."
Members of the IPR agree to adhere to a code that includes a promise to "maintain the highest standards of professional endeavour, integrity, confidentiality, financial propriety and personal conduct".
The resignation could prove devastating for Mr Harkin should he wish to resurrect his PR career.
Executives do not have to be members of the institute but membership allows clients to make sure codes of conduct and standards of practice are adhered to.
The "fake sheikh" sting was carried out by the undercover News of the World reporter, Mazher Mahmood, in April.
He revealed Mr Harkin had tried to cash in on Sophie Wessex's royal connections and made public the countess's embarrassing remarks about royals and politicians.
• This article, and the headline, were amended on 19 December 2014 to clarify that the IPR accepted Murray Harkin's resignation, rather than expelling him.
