A merger between Fiat Chrysler and French automaker Renault seemed like a pretty sure thing at the beginning of the week, but both companies announced the idea is completely dead.

The conventional wisdom holds that Fiat Chrysler withdrew the offer because a French government representative had requested a postponement.  The French government owns more than 15 percent of Renault, making it the company's biggest shareholder.

But the Wall Street Journal reported that Nissan threw a spanner in the works as bitterness increases between Renault and Nissan - Renault owns 43 percent of the Japanese automaker, and Nissan  owns 15 percent of Renault.  

"The idea you would negotiate a merger without speaking with your 20-year partner is absolutely extraordinary," a source familiar with the negotiations told the WSJ.  "It's about trust, and that’s the problem here."