Yet another top aide has departed 10 Downing Street, just days after the exits of the Prime Minister's two most senior advisers.
The deputy head of May's policy unit has left after just over a year advising May.
Formerly of think tank Reform, Will Tanner joined May's officials while she was in the Home Office, following her to Number 10 after the Brexit referendum.
A party source paid tribute to Tanner, labelling him "immensely talented". "He has given great service and we wish him well," they said.
The news comes just days after May's joint chiefs of staff, Nick Timothy and Fiona Hill, quit last week following a disastrous General Election campaign during which the Conservative Party lost a total of 13 seats.
Timothy has since resurfaced with a high-profile attack on "campaign consultants" Lynton Crosby and Jim Messina in an article for the Spectator.
Crosby ran the Tories' 2015 campaign, while Messina was an adviser to former US President Barack Obama.
Timothy hit out at his advice to put May, rather than her whole team, at the forefront of the campaign.
"Lynton Crosby's last text to me predicted that we were going to 'do well', which according to our expectations would mean a majority of more than 60," Timothy wrote.
"A late projection, based on data from the ground and Jim Messina's modelling, suggested we would win 371 seats, giving us a majority of 92," he added.