The announcement violates the unspoken protocol among Spain's royalty and marks Letizia's most recent attempt to win over the public's hearts and break from the country's staunch traditions, said The Sunday Times of London.
The 34-year-old former TV journalist has long attempted to maintain her connection with Spain's working class, and her openness regarding her non-traditional ways have angered many of the country's "Juan Carlistas," fierce supporters of conservative King Juan Carlos.
The impending child would be the second for Letizia and her husband, who is the heir to the Spanish throne. Their daughter Leonor was born 11 months ago.
Notable deaths of 2014 [PHOTOS]
Polly Bergen, Emmy Award-winning actress, dies