The castle, located on the southern coast of Zealand facing across the Baltic Sea towards Germany, was originally built in the 12th century by King Valdemar the Great.
Valdemar used it as a base for raids on Germany and, later under Valdemar's son Valdemar II the Victorious, Estonia.
The castle was then expanded during the 14th century by the third Valdemar, Valdemar the Younger.
The three Valdemars have since been considered the original lords of the castle and given credit for making it one of the most impressive sights in the country.
But recent archaeological work has now revealed that much of the fortification work was carried out by Valdemar the Great's eldest son King Canute VI, who reigned between the first and second Valdemars.
"Traditionally, Valdemar the Great is seen as the founder, with Victorious and Younger later expanding the castle. Other kings of the period are not given a lot of credit, but our excavations have revealed that Canute VI has played a greater role than previously thought," Lars Sass Jensen, medieval archaeologist and research assistant at Aarhus University, told Jyllands-Posten.
During their excavations, Jensen's team discovered wood that they were able to exactly date to the years 1189-90, 1195 and 1198-99 - years in which Canute ruled the castle and Denmark.
"He didn't just build over the castle, he expanded it continuously. He was, in other words, a king that invested heavily in the site as well as in its political function as a base for Baltic Sea expansion," Larsen said to Jyllands-Posten.