Publicis CEO Maurice Levy has told CNBC that the decision to call off a $35 billion merger with U.S.-based Omnicom was "an issue of principle."
In an exclusive interview, Levy said the deal had been presented as a merger of equals, but that in the end, it was impossible to get equality.
The companies had planned a 50-50 ownership split of the equity in the new firm, with Omnicom head John Wren and Levy serving as co-CEOs for 30 months. But Levy said that equality in the management team was not part of Omnicom's eventual proposals.
Read MoreOmnicom, Publicis call off proposed $35 billion merger
"I was going back and forth to try to convince them (Omnicom) that we should have equality; it was impossible to get that equality and this was not the terms of the agreement," Levy told CNBC.
He also said that the deal posed a threat to Publicis' business model, which was to be focused on delivering the highest margins in the industry.
"We had the feeling that, in fact, that model may be diluted and the promise that we made to the market - that we would deliver superior margins - would not be met," Levy said.
As the world's largest pharmaceutical company Pzifer attempts to acquire AstraZeneca, Levy was asked whether a merger of equals was more difficult to implement than a takeover.
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"Definitely yes," he said. "(In) an acquisition, you are the master, you make your decision - people are acquired and they have no say. (In) a merger of equals, you have to share; to discuss almost every single decision. It's more complicated, definitely."
British advertising group WPP's CEO spoke to CNBC following the collapse of the deal, and said it had been driven by ego and emotion.
"It was turning into a bit of a soap opera because both companies in their Q1 statements were saying they were good on their own," WPP boss Martin Sorrell told CNBC.
Read MoreOmnicom, Publicis deal was driven by ego: WPP
"I think this deal was driven by ego issues and emotional issues… It was also a case of eyes being bigger than your tummy," he added.
Levy responded to Sorrell's comments, saying the rival CEO has some "nice expressions."
"So next time he is sending me an email or SMS saying that he would like to be the CFO (of Publicis) I will think twice," he said.