The French magazine Point de Vue reported the 50-year-old reputed former playboy intends to marry Wittstock, 30, in Monaco later this year.
"While the date is not yet fixed, two sources confirm that preparations are under way for a royal wedding at the end of the summer," the Daily Telegraph quoted the French magazine as saying.
The Mediterranean principality has not celebrated the wedding of a ruling prince since 1956, when Prince Rainier, Albert's father, married Hollywood icon Grace Kelly, the Telegraph noted.
Beautician charged with giving client fatal silicone butt injection
Duggar sisters unveil Christian dating rules in new book