Reed, who played Mike Brady on the hit U.S. Tv series, was gay but kept his sexuality a secret for years over fears it would damage his career and reputation.
He passed away after a six-month battle with colon cancer in 1992 but the actor was also Hiv postive, which doctors listed as a "significant condition contributing to death".
Now Olsen has spoken out about the man she hails as "another father figure", his struggle to cope with his sexuality and her support of gay marriage as U.S. Supreme Court officials debate the hot topic in Washington, D.C.
In a lengthy post on her official Facebook.com page she writes, "As a child, I was Blessed to have another father figure in my life. He did not replace my own beloved (father) nor would he have wanted to. He simply harmonized with all of my family values and brought his own heart to our table. This wonderful man was a giant in my world, a true king among men. His name was, and is, Robert Reed...
"So I really can honestly say, 'My Dad was Gay'. I can also say that being gay killed him. Because it was so taboo, he could never make peace with himself. He never allowed himself to have a genuine love. He was forever taunted by his own disdain for the natural inclinations that he was Born With.
"Bob was a family man. Had he been allowed to form a relationship with another man, he would have been the best husband ever and might still be alive. But Bob could not be at peace with this because the people surrounding him shoved their own judgement down his throat and, sadly, he bought into it. He thought he was wrong...
"If two people love each other enough to want their union consecrated by a mythological being (God) - they are undoubtedly insane, but LET THEM HAVE AT IT!!!!"
U.S Supreme Court officials have yet to reach a decision on whether or not to throw out California's Proposition 8, the legislation outlawing same-sex marriage in the state.