The royal palace has lodged a complaint with a media ethics group over the publication of a book highlighting alleged dalliances and private family information about leading members of Belgium's monarchy.

Wednesday's rare move by the palace came after the publication last week of the book "Royal Questions" by journalist Frederic Deborsu, in which suggestions were made, among others, about the lack of love within the marriage of Crown Prince Philippe.

The crown prince himself already made an equally rare reaction last week, saying: "The day that Mathilde said 'yes' to my proposal was the happiest day of my life."

Deborsu's employer, the public broadcaster RTBF, said he will be barred from appearing on the TV channel for at least a month but refused to call that a penalty.