Simplify the following text for a Grade 10 native English-speaking person.
Original: Saint-Denis ( or unofficially Saint-Denis de la RÃ union for disambiguation ) is the prÃ fecture ( administrative capital ) of the French overseas region and department of RÃ union , in the Indian Ocean .
Simplified: Saint-Denis is the administrative capital ( prÃ fecture ) of the French controlled island of RÃ union , in the Indian Ocean .