For most of his life, the crown prince has been seen as a less-than-credible successor for his father, who is now 78.
Philippe was considered aloof and awkward, with the charisma of a civil servant. Until his engagement a dozen years ago, he was seemingly headed for terminal bachelorship.
"The general perception is that he is not up to the job to become king," Reynebeau said. "Nobody knows, of course, because it is all speculation."
King Albert, who succeeded his brother in 1993, saw his own image darkened a dozen years ago when he had to acknowledge that he had fathered a daughter out of wedlock.
The scandal caused by Deborsu's book comes on the heels of a major municipal election victory by the separatist N-VA party in northern Flanders last month. The party aims to break up the bilingual nation along linguistic lines and is already looking forward to nationwide elections in 2014.
If the country breaks up, Belgium's royal house would become obsolete.