Tory councillor Derek Wann, who has fronted anti-bullying campaigns on behalf of Angus Council was revealed to be the owner of the "(Lady Whistledown) AngusFreeofSNP" account following an investigation by The Courier.
The account, styled after the anonymous newsletter-writing gossip from Netflix series Bridgerton, was followed by some members of Angus Council before its deletion earlier this week.
Cllr Wann used the account to challenge members of the public who interacted with his public persona on Twitter, and dished out abuse aimed at female and opposition politicians, including one tweet where he branded First Minister Nicola Sturgeon a "******* ned".
He even turned his vitriol against his own region, poking fun at the town of Brechin on several occasions.
The SNP has challenged Mr Ross to take disciplinary action against the councillor.
SNP MSP Rona Mackay said: “There is no place in politics for such obnoxious and sleekit behaviour. Derek Wann’s conduct is absolutely indefensible, particularly in mocking drugs deaths.
“This is a serious test of Mr Ross’ leadership – he must act without delay. There is no need for an investigation when the man at the centre of it all has already admitted his atrocious behaviour."
Cllr Beth Whiteside, SNP group leader, said his position was "completely untenable".
She said: "Cllr Derek Wann reveals his Jekyll and Hyde personality, with the revelation that he is the man behind the poisonous 'Lady Whistledown' Twitter account.
"The Angus Council senior councillor and convener of the children and learning committee, who has publicly pledged support for the 'ThinkB4UType' anti-bullying campaign, reveals himself to be nothing more than an anonymous online troll.
"Surely his position is now completely untenable."
Ben Lawrie, Liberal Democrat councillor for Monfieth, said: "The unmasking of Lady Whistledown as a senior administration figure further illustrates the unhealthy culture at the top of Angus Council.
"Cllr Wann’s position as convener of children and learning is no longer tenable. He must resign."
However, Cllr Wann appears to have retained the full confidence of Angus Council leader David Fairweather, who followed and interacted with the anonymous account. It is not known whether he was aware of the true identity of the account holder.
Cllr Fairweather said today: "Cllr Wann is a Conservative member and as such this will be investigated by that party.
"I have had a conversation with Cllr Wann and that will remain private.
"All senior councillors in their specific roles with extra duties working with council officers are remunerated accordingly as with other authorities.
"Derogatory comments that I have seen written are not recognised by myself as to how the administration runs."
Cllr Wann accidentally exposed himself as the owner of the account when it posted a link to a press release on the Angus Council website in which he was quoted, and captioned the link: "My comments."
He sought to cover his tracks after this was pointed out by linking to another press release quoting communities convener Cllr Mark Salmond with the same "My comments" caption.
After The National newspaper linked Cllr Wann's phone number with the Lady Whistledown account, he took the feed offline, but continued to deny he was behind it.
While the account has been removed, many of the tweets remain accessible via the Internet Archive. The Scottish Conservatives have launched an investigation.
Cllr Wann, who represents the Arbroath East and Lunan ward, said last night: "I apologise sincerely for how I have handled this matter. My actions were unacceptable. I have now provided the party with the relevant facts so they can conduct an investigation."