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He said in a letter to staff that the "current disruption" was "putting too much unnecessary pressure on the business," Reuters reported.
Sorrell has previously denied the allegations, but said he recognized the need for WPP to launch an investigation.
To read more about Sorrell's resignation, click here.
In related news:
Here's the full letter Martin Sorrell sent WPP staff after standing down as CEO. "As a Founder, I can say that WPP is not just a matter of life or death, it was, is and will be more important than that," he wrote.
The chance of WPP being broken up has 'dramatically increased.' Read how Goldman, UBS and other major analysts are reacting to Sir Martin Sorrell leaving.
In other news:
A digital-media veteran spent $350,000 to fly hundreds of publishers to Whistler, Canada and recruit them to battle Facebook. Led by serial entrepreneur Jim Heckman, Maven is trying to build a coalition of small digital publishers to join a common tech platform and reclaim some of the audience and ad budgets swallowed up by Facebook.
Two Facebook pages associated with neo-Nazi Richard Spencer have been removed from the site. Pages for the National Policy Institute, run by Spencer, was removed, as was a page for his online magazine "Altright.com."
Starbucks CEO apologizes to the two black men arrested in a Philadelphia store, says he wants to meet with them 'face-to-face.' Several videos that went viral showed police officers handcuffing two men and leading them out of the store, over the protestations of bystanders who said "they didn't do anything."
A study has found lots of apps on Google Play are violating the "COPPA" rules intended to protect children from online advertising. It suggests kids are being profiled and targeted by online ads.
Tronc's largest shareholder, Michael Ferro, has agreed to sell his stake in the business. Ferro has sold his shares to a relative of the McCormick family that built the company's flagship newspaper, the Chicago Tribune, into a media powerhouse.