Dawn Neesom has left her role as editor of the Daily Star after 15 years.
In a farewell message to staff, seen by the Press Association, Ms Neesom said she was leaving as of Wednesday night for “new challenges”.
Her departure comes just weeks after the publisher of the Daily Mirror struck a £126.7 million deal to buy a string of titles from Richard Desmond’s media empire, including the Star, Daily Express, and OK! magazine.
A source at the Star said Ms Neesom’s email “came from nowhere” and company executives were expected to address staff on Thursday.
In her memo to staff, Ms Neesom said: “After 15 years as editor of this brilliant newspaper I’m out of here as of tonight.
“I will miss you all hugely, but never forget that you are a fantastic team who have talent, guts, determination and, above all, one another.
“I’ve been the longest serving editor of the Daily Star, the longest serving female national newspaper editor and taken sales to their highest in the paper’s recent history.
“It’s been an incredible experience, but it really is the time to move on to new challenges.
“I wish all of you the very best of luck in the future.
“So thank you all once again for being a bloody amazing bunch of people to work with. ”
Ms Neesom, who was among a small number of women editors at national newspapers, last made the headlines during her appearance at the Leveson Inquiry.
She told the inquiry that entertaining readers “doesn’t necessarily mean you can just make a story up”, insisting stories have to be “accurate and true”.
Under the deal struck in February, Trinity Mirror will stump up an initial payment of £47.7 million to Northern & Shell, followed by £59 million between 2020 and 2023 and a further £20 million in shares to the privately-owned firm.
The move marks a major shake-up of Britain’s media landscape, bringing together politically left-leaning titles such as the Sunday Mirror, with more right-wing publications such as the Sunday Express.
Trinity Mirror chef executive Simon Fox ruled out a shift in editorial tone.
Speaking to the Press Association at the time, he said: “The titles have separate editors and they know their readers best and have full control over the content – that will not change.”
Circulation of the two flagship titles have also come under pressure, with the Daily Express and Daily Star falling 6.8% and 11.1% respectively in December.