Sir Martin Sorrell, the founder and chief executive of advertising giant WPP, has said a Brexit vote "is not good news, to say the least".
Sorrell, who spoke out against the prospect of a Leave vote on numerous occasions, said today he is "very disappointed".
And he raised fears over what impact Brexit will have on the advertising industry.
On Friday morning, WPP's shares plunged by around six per cent to 1,497p.
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"The resulting uncertainty, which will be considerable, will obviously slow decision-making and deter activity," Sorrell said.
"This is not good news, to say the least. However, we must deploy that stiff upper lip and make the best of it."
Sorrell also told of the need for WPP to enhance its operations on the continent.
He said: "Four of WPP’s top ten markets are in Western Continental Europe and we must build our presence there even further.
"It just underlines the importance of implementing our strategy: fast-growth markets (BRICs and Next 11), digital, data – and horizontality, which ironically means getting our people to work together, not apart!"