A cursed kingdom inhabited by both mortals and magical beings.
Tarsina is a fictional kingdom in the non-canonical novel, The Queen's Curse. The country is located somewhere in Switzerland, inhabited by magical and mortal residents. Because the kingdom exists exclusively in its own realm and few ever left the land, magical creatures in the outside world thought it to be a myth.
For centuries, the people of Tarsina lived in peace, invisible to mortals, except when invited by an inhabitant.
The 20th century
In the 20th century, locals began to venture out to the world to explore. Some of them returned with mortal spouses. The queen of that generation was furious with the idea and cast a curse on the entire kingdom where the throne prince or princess must marry a pure magical being on his or her 25th birthday at latest or every mortal inhabitant in the kingdom will die. The queen passed away in 1916.
For generations, many royal members had fought to keep the curse from enacting, though there were also those who worked against them, hoping that by enacting the curse, the kingdom will be free of mortals once again.
Lifting the Curse
In the early 21st century, crown prince Colin sought to marry Paige Matthews, a Charmed One, to preserve his kingdom. The curse's loyalists, including Colin's mother, plotted to stop the marriage, but the sisters managed to gather the entire kingdom's people and unite their magic to break the curse once and for all, allowing Colin to marry his true love: the mortal Corinne.