THE tenure of Carlos Ghosn, the boss of both Japan's Nissan and France's Renault, is unprecedented. No other big multinationals have shared a boss. Nor is the feat likely to be repeated. Though Mr Ghosn has performed well over the past decade, it is hard to imagine another executive having the credibility to take over two proud companies with such distinct national cultures. It took the consummate outsider—a Brazilian-born Frenchman of Lebanese descent, raised in the Middle East—to succeed, in addition to a talent for making cars.

Now that Mr Ghosn has been approved for another two years as Nissan's boss, at its annual shareholder meeting on June 29th, it is appropriate to consider who might follow him. It is not idle speculation. Mr Ghosn's contract at Renault expires in 2014. His latest one at Nissan finishes around then too. It is certain that over the next two years Mr Ghosn and both company boards will prepare his succession.

The most probable way of going about this is to create an "alliance board" of delegates from each company. The board would start shadowing Mr Ghosn while he is still occupying the corner office at each firm's headquarters. It would co-ordinate all aspects of the partnership, from joint procurement and design of shared parts to the equity stakes they hold in each other. Later, when separate chief executives are appointed for each company (as is almost certain), these will join the board to oversee the joint operations.

In addition to managing the transition, Mr Ghosn has his work cut out for him over the next two years. He must restore Renault's shine, after its recent loss of market share in Europe and a horrible gaffe in which he wrongly dismissed three veteran managers over false allegations of intellectual-property theft. Nissan, in contrast, enjoyed record sales last year and overtook Honda to become Japan's second-biggest carmaker. But Mr Ghosn still has ambitions for the Japanese part of his dual empire: he wants to see its global market share rise to 8% by 2016 (from 5.8% in 2010) and its operating margin also at 8% by then (from 6.1%).

Until now, the Nissan-Renault alliance has largely worked because it has been led by one person who enjoys credibility within both companies. Once he is leaves, and is replaced by a committee, it is not certain that things will go so smoothly. He will be a hard act to follow.

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