You heard because El heard and shared and some right-wing anti-Chavez 'expert' made it up for you to hear and share. This story is two years old, the Castro story is 5-7 years old at least....and no compelling evidence or paper-trail has ever been produced.
As a journalist of 25 years experience I would like to think people actually check out what they hear rather than believe any old made up BS.
We all have a responsibility to check sources for credibility. Investigate, particularly when the source comes from someone whose views are diametrically opposed to the person they are accusing.