Many details remain unclear, but Martin Sorrell's departure from the marketing giant that he built over decades arrived abruptly, coming just 11 days after WPP confirmed that it was looking into an unspecified allegation against him.
Sorrell's exit caps a remarkable turnaround for the 73-year-old, whose iron grip on WPP helped characterise its rise into the world's largest advertising company.
Said he: "I shall miss all of you greatly".
The firm said that "the allegations do not involve amounts which are material to WPP".
The Wall Street Journal reported that the investigation targeted whether Sorrell "misused company assets".
"To me it's not actually about whether he did anything wrong but it's the fact that three years ago the board would not even have gone down this path", the former CEO said.
Sir Martin was born in London and educated at the Haberdashers' Aske's Boys' School before going on to read Economics at Christ's College, Cambridge.
WPP, then Wire and Plastic Products, was a United Kingdom manufacturer of wire baskets for the first 14 years of its life until 1985 when Sir Martin took a loan out against shares he owned in Saatchi & Saatchi and purchased a stake in the company after seeking a public entity through which he could build a marketing company.
Respected by his peers, he was however shown little affection by them in the ego-driven ad business and was sometimes dismissed as a "beancounter" because of his financial rather than advertising background. So if WPP does well, I do well, and others in the company do well.
He faced a limited shareholder revolt in 2015 after receiving a £70.4 million remuneration package. "He is such a competitor and he can get so angry when he loses".
One of UK's top-paid executives. One New York-based executive told Reuters how, on a night out, senior executives would all email Sorrell at exactly the same time to see who he would respond to first. "It's practically a stage show".
CEOs and executives, who asked not to be named, lamented that Sorrell would not get the chance to reposition WPP, which in March posted its weakest results since the financial crash.
Some multinational advertisers, including P&G, which owns Ariel and Gillette, have signalled their intention to take more of their marketing services activity in-house, reducing the lucrative work for which they are charged by external agencies.
Shares in WPP are expected to fall tomorrow when the markets open. Meanwhile, WPP Chairman Roberto Quarta will run the agency until a new CEO is chosen. Said Sorrell in his note: "We have had a succession plan in place for some time".
Sorrell, via a statement from his crisis PR rep Project Associates, said he's sad to leave WPP. "Good fortune and Godspeed to all of you...now Back to the Future".