Princess Catharina-Amalia of the Netherlands appeared on the balcony of the Noordeinde Palace alongside King Willem-Alexander, Queen Maxima, Princess Ariane and Princess Alexia Patrick van Katwijk/Getty ImagesIt's one of the most important days in the Dutch calendar – and while crowds may have gathered to celebrate across the Netherlands to celebrate Prince's Day, it was the royal daughters who stole the show. Princess Catharina-Amalia, the heir to the Dutch throne, was joined by her sisters, Princesses Alexia and Ariane, on the balcony of the Noordeinde Palace alongside their parents, as they marked the traditional opening of parliament. King Willem-Alexander and Queen Maxima beamed as they waved to the crowds from their home in The Hague, the King wearing smart morning dress and his wife co-ordinating in a subtle, pale-grey dress with a draped neckline, which she matched with a dramatic hat and clutch bag. In September every year, the King delivers a speech from the throne which officially opens the parliamentary year, and sets out the government's plans for the year ahead. The royal procession, which sees the family travel through the streets of The Hague in a glass carriage, is always well-attended by crowds and, this year, locals turned out in force to catch a glimpse of the royals.