Knight and his costar Susan Olsen pointed out that the writers even 'forgot' the kids weren't related at one point ...

The “Brady Bunch” cast has revealed why the classic sitcom never explained what happened to Carol Brady’s first husband — despite being more forthcoming about Mike Brady’s first wife.

Brady Bunch star Susan Olsen ... bad enough that they could still be seen in subsequent episodes and publicity photos, including during the wedding between mother and father Brady.