Meyer, who has headed Grey since 1970, sold 16.9m shares at 624p each, raising 拢105.5m.
WPP paid $1.7bn (拢890m) for Grey, half in cash and half in shares. According to reports, Meyer's sale of 16.9m shares represents almost all of the WPP shares he received in the deal.
The swiftness of the sale has prompted speculation that Meyer may be unhappy with his role in the new company. WPP has said that Grey will continue to be run as a separate entity, headed by Meyer, but he must find someone to take over as chief executive within the next six months.
However, the sale could also be part of moves by Meyer, who is aged 78, to get his estate in order. The sale of Grey has made Meyer an extremely wealthy man, giving him payouts worth over $75m on top of money he received for his shares. He still receives a $1m salary.
WPP's share price fell by 2% on news of the sale, down by 2.5p to 623p yesterday, and falling a further 3p when the market opened this morning to 620p.
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