He added that his request for dual French-Belgian citizenship is “linked to personal reasons."

Indeed, tax lawyers say they are hard-pressed to find the tax benefits of Arnault’s proposed Belgian citizenship if he remains a tax resident. In France, tax obligations are determined by residency rather than citizenship. (Read more: Mass Migration of the Super-Rich )

Arnault says he will remain a resident of France, so he would still be subject to all or nearly all French taxes, lawyers say. That includes Hollande's proposed 75 percent tax on people making more than euros a million a year, as well as France’s wealth tax, inheritance taxes and real estate taxes, according to Jonathan Chazkal, a partner of the Belgian law firm Afschrift, which specializes in tax law.

In fact, Belgium’s income-tax rate of more than 50 percent is currently higher than France’s rate of around 45 percent. Lawyers say that if Arnault wanted to change his residency to avoid French taxes, he could become a Belgian resident at any time without becoming a Belgian citizen, which is far more difficult.

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