Juventus star Ronaldo, 34, bought the flat in the Portuguese capital of Lisbon in July of last year but news of its purchase has only recently surfaced.
The former Real Madrid star reportedly won a tough bidding war against two other millionaires in order to purchase the £6.1m (€7.2 m) luxury flat in the Castilho 203 building in the Avenida de Liberdade area of the city.