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Princess Diana smiles at the premiere of the film "Indiana Jones and the Temple of Doom", June 1984. She is pregnant with her second child. (AP Photo)

A six-month pregnant Princess Mathilde from Belgium walks to the gala dinner May 20, 2003 in Brussels, Belgium. King Harald and Queen Sonja from Norway are in Belgium for a three-day state visit during which time they will visit the Brussels, Flemish and Wallon regions. (Photo by Mark Renders/Getty Image)

Eight months pregnant Princess Mathilde of Belgium talks to Russian Commander Serguey Zaletin on July 1, 2003 at the Royal Palace in Brussels, Belgium. The Belgian Kingdom received the astronauts of the Odissea Mission in presence of Commander Serguey Zaletin and Colonel Frank De Winne. (Photo by Mark Renders/Getty Images)

Belgium's Princess Mathilde attends an information day on breast cancer for immigrant women on February 16 2008 in the Elzenveld Cultural Conference Center in Antwerp. Princess Mathilde, wife of Crownprince Philippe, is pregnant with her fourth child. LIEVEN VAN ASSCHE/AFP/Getty Images

Princess Mathilde of Belgium arrives for a visit to Katholieke Hogeschool Kempen, in Vorselaar on February 28, 2008. Mathilde, wife of Crownprince Philippe, is pregnant with their fourth child. LUC CLAESSEN/AFP/Getty Images

Belgian Prince Philippe (C) and Belgian Princess Mathilde (R), pregnant with her fourth child, welcome Prince Charles of Britain (L), 13 February at the Royal Castle of Laeken-Laken, in Brussels region. Prince Charles is on a two-day visit to Brussels. JOHN THYS/AFP/Getty Images

Crown Prince Willem-Alexander (L), 36, and his Argentinian wife Princess Maxima (R), 32, leave the Binnenhof, 18 June 2003, in the Hague, after revealing Maxima's three-months first pregnancy. AFP/Getty Images

Prince Willem-Alexander of the Netherlands and his pregnant wife Princess Maxima of the Netherlands visit Middle East Technical University (METU) on February 28, 2007, in Ankara, Turkey. The Dutch royal family arrived in Ankara on Tuesday for a four-day official visit to Turkey. (Photo by Stringer/Getty Images)

Prince Willem-Alexander of the Netherlands and his pregnant wife Princess Maxima of the Netherlands visit Middle East Technical University (METU) on February 28, 2007, in Ankara, Turkey. The Dutch royal family arrived in Ankara on Tuesday for a four-day official visit to Turkey. (Photo by Stringer/Getty Images)

Crown Princess Maxima of Holland holds her hand on her stomach as she officially opens the new FMO Development Bank building September 12, 2003 in The Hague, Netherlands. Crown Prince Willem Alexander and Princess Maxima are expecting their first child in January. (Photo by Michel Porro/Getty Images)

Dutch Princess Maxima arrives at the King Willem I College to attend a ceremony in which the school received a No Racism Certificate on May 19, 2005 in Den Bosch, the Netherlands. Princess Maxima is pregnant with her second child which is expected in June (Photo by Michel Porro/Getty Images)

The pregnant Princess Maxima enters the Binnenhof with Prince Willem Alexander September 16, 2003 in The Hague, Netherlands. Queen Beatrix traditionally gives a speech to mark the state opening of parliament in the presence of members of the Dutch government and the rest of the Dutch Royal family at the Binnenhof in The Hague. (Photo by Mark Renders/Getty Images)

Princess Maxima, Prince Willem Alexander and Queen Beatrix sit in the golden carriage on their way to Palace Noordeinde September 16, 2003 in The Hague, Netherlands. Queen Beatrix traditionally gives a speech to mark the state opening of parliament in the presence of members of the Dutch government and the rest of the Dutch Royal family at the Binnenhof in The Hague. (Photo by Mark Renders/Getty Images)

Princess Maxima, Prince Willem Alexander and Queen Beatrix wave to the gathered crowds from the balcony September 16, 2003 in The Hague, Netherlands. Queen Beatrix traditionally gives a speech to mark the state opening of parliament in the presence of members of the Dutch government and the rest of the Dutch Royal family at the Binnenhof in The Hague. (Photo by Mark Renders/Getty Images)

Spanish Royal Crown Prince Felipe and Princess Letizia receive an audience with the Lawyers General Council and the National Press Association at Zarzuela Palace on September 6, 2005 in Madrid, Spain. (Photo by Carlos Alvarez /Getty Images)

King of Spain Juan Carlos de Borbon reacts after being asked by journalists about the official announcement of their daughter Infanta Cristina's pregnancy, 09 December 2004, during a visit to inaugurate a new factory in the northern Spanish Basque village of Mondragon. RAFA RIVAS/AFP/Getty Images

Prince Felipe of Spain and his wife Princess Letizia of Spain attend the Christening of their niece, Princess Irene, the daughter of Princess Cristina of Spain (the Duchess of Palma), and her husband Inaki Urdangarin at the Palacio de la Zarzuela on July 14, 2005 in Madrid, Spain. The royal couple's first girl and fourth child is ninth in the line of succession to the throne. (Photo by Angel Diaz/Getty Images)

This picture taken 12 October 2005 shows Spain's Princess Letizia (C) arriving with her husband Prince Felipe for the national day army parade in Madrid. Princess Letizia, the eight-and-a-half-months pregnant wife of Spanish heir to the throne Prince Felipe de Bourbon, was admitted to a private maternity clinic 30 October 2005 on medical advice, the royal palace announced. JAVIER SORIANO/AFP/Getty Images)

Spain's Prince Felipe (R) salutes next to his wife Princess Letizia as they watch the national day army parade in Madrid. Princess Letizia, the eight-and-a-half-months pregnant wife of Spanish heir to the throne Prince Felipe de Bourbon, was admitted to a private maternity clinic 30 October 2005 on medical advice, the royal palace announced. JAVIER SORIANO/AFP/Getty Images

HRH Crown Princess Mette-Marit of Norway attends a literary luncheon at The Groucho Club as part of her 3 day visit to the UK to mark 100 years of Norway's independence from Sweden, on October 25, 2005 in London, England. (Photo by Gareth Cattermole/Getty Images)

HM Queen Sonja of Norway and HRH Crown Princess Mette-Marit of Norway attend a literary luncheon at The Groucho Club as part of their 3 day visit to the UK to mark 100 years of Norway's independence from Sweden, on October 25, 2005 in London, England. (Photo by Gareth Cattermole/Getty Images)

Danish Crown Princess Mary, who is pregnant with twins, tours Schloss Guestrow palace with her husband Danish Crown Prince Frederik on September 28, 2010 in Guestrow, Germany. Prince Frederik and Princess Mary are on a two-day visit to northern Germany. (Photo by Sean Gallup/Getty Images)

Danish Crown Prince Frederik and Danish Crown Princess Mary, who is pregnant with twins, greet onlookers upon their arrival at the High School for Music and Theater on September 28, 2010 in Rostock, Germany. Prince Frederik and Princess Mary are on a two-day visit to northern Germany. (Photo by Sean Gallup/Getty Images)

Catherine, Duchess of Cambridge meets 5 month-old James William Davies, who was named after Prince William, and his mother Tessa Davies in the Market Square during an official visit to the Guildhall on November 28, 2012 in Cambridge, England. (Photo by Arthur Edwards - Getty Images)

Pregnant Sweden's Crown Princess Victoria (R) and Prince Daniel arrive for a lunch at Stockholm's Royal Palace on February 21, 2012. PONTUS LUNDAHL/AFP/Getty Images

Crown Princess Victoria of Sweden touches her pregnant belly at the Nobel Prize Banquet at Stockholm City Hall on December 10, 2011 in Stockholm, Sweden. (Photo by Pascal Le Segretain/Getty Images)