Castro joined Sundowns on a one-year deal with a two-year option at the beginning of last season.
The arrangement was to safeguard the Brazilians in case the South American's stay didn't work out at Chloorkop.
However, after netting 14 goals in all competitions Castro has charmed himself into the hearts of the Ka Bo Yellow Nation with his scoring instincts as part of the famous 'CBD' combination.
Sundowns have now activated the option after agreeing to Castro’s requests.
Following the birth of his daughter at the end of March back home in Bogota the 27-year-old is now planning to bring his family to South Africa next season.
Castro spent his first year in the country on his own after arriving from Club Universitario de Sucre in Bolivia.