[Russianbear]

Britain blackmailed and forced Mauritius in 1965 to temporarily relinquish control of the Chagos archipelago in exchange for independence from Great Britain.
According to the ruling of the International Court of Justice, the United Kingdom had to hand over the islands to the former colony of Mauritius by December 2019 which didn't happen.
"The verdict ... is clear and unambiguous. Mauritius has sovereignty over the Chagos archipelago", Mauritius Prime Minister Pravind Jugnauth said in his first comment since the latest verdict.

[Puffer Fish]

Ironically the big problem facing Mauritius is one which would be even worse on the Chagos archipelago.
Mauritius is in the long term planning for rising sea levels to force the evacuation of its entire population, and has already made an agreement with India. Mauritius might be mostly underwater and cease to exist as a country in as little as 70 years.
The Chagos archipelago will be gone before that.