'Brady Bunch' star Christopher Knight on why his late TV father Robert Reed was so impactful (exclusive)

It was 50 years ago that the kids of the "Brady Bunch" became a family both on- and off-screen.

Half a century later, all six of the now-grown Bradys were on hand for HGTV's "A Very Brady Renovation," where they helped to transform the real California house that served as their faux home's exterior. Throughout the four-part special, the cast reminisces about the beloved co-stars they've lost along the way.

Christopher Knight, who played middle son Peter Brady, spoke with AOL exclusively about Robert Reed, the actor who brought to life his TV dad Mike Brady. "As I would grow older, I would learn — even after his passing, looking back with adult eyes — how impactful he was," he said. "I couldn't put it into perspective until years later."

Reed, who died in 1992, had a complicated relationship with "The Brady Bunch." A trained Shakespearean actor, he was deeply frustrated with the sitcom from day one; he found the plots to be frivolous and wanted to create a more dynamic, true-to-life family program. In addition to his career agitations, he privately struggled with his sexual orientation and subsequent HIV diagnosis, which his co-stars would later say contributed to his unhappiness.

But while Reed famously sparred incessantly with creator Sherwood Schwartz, he had positive relationships with his castmates. Knight still vividly remembers a particular day during his early teenage years when Reed, who was directing an episode, spoke to him not as a kid but as an actor.

"Most ["Brady"] directors, for the sake of getting done on time, would have us kids line up shoulder-to-shoulder. Nothing about it was organic. It always felt a little stilted to me," Knight recalled to AOL. "But Bob Reed said to me, 'What do you see yourself doing right here?'"

Knight was stunned. "He's asking me!" he said. "I remember being taken aback — big inhale, like, he's asking me my opinion."

Schwartz only occasionally allowed Reed to direct episodes: "Of course, Bob's episodes were notoriously late, because they were more artistic," Knight said. "But as a young kid who hadn't gotten this at home, that my point of view had validity and should be part of the equation, something that hadn't been gifted me by my own parents yet in my own world ... And I sure did have an opinion, and he figured out how to shoot it."

He added, "It riveted me that day, working with Bob."

Reed never publicly came out, and his death at 59 was initially attributed to colon cancer. It was later revealed that his HIV-positive status significantly accelerated his passing. Florence Henderson, who played Carol Brady, would speak candidly about her on-screen husband a few years later, in 2000.

"Here he was, the perfect father of this wonderful little family, a perfect husband. Off camera, he was an unhappy person – I think had Bob not been forced to live this double life, I think it would have dissipated a lot of that anger and frustration," she told ABC News. "I never asked him. I never challenged him. I had a lot of compassion for him because I knew how he was suffering with keeping this secret."

The blue-walled bedroom that Mike and Carol Brady shared is among the rooms that are recreated "A Very Brady Renovation," which airs its third episode Monday night on HGTV.

RELATED: Watch an exclusive clip from "A Very Brady Renovation"