Read the text and determine if the sentence is true:

Albert II (Albert Alexandre Louis Pierre Grimaldi; born 14 March 1958) is the reigning monarch of the Principality of Monaco and head of the princely house of Grimaldi. He is the son of Prince Rainier III and the American actress Grace Kelly. Prince Albert's sisters are Caroline, Princess of Hanover, and Princess Stephanie. In July 2011, Prince Albert married Charlene Wittstock.

Sentence: Who mothered Albert II is unknown to the society.
No