Are you referring to a statement from Peter Van Mol (Big Cat).. Where he describes nandrolones estrogenic response via AR:
I remember that discussion. I'm a little dubious about estren being responsible for the oestrogenic sides of nandrolone. In so far as it's a metabolite, it's pretty minor and appears to convert back to nandrolone very rapidly. The idea that nandrolone activates oestrogen response elements (ERE) through the AR seems very credible though.
But in either case I don't think either estren or nandrolone's ERE effects via AR could entirely account for the joint effects we notice, otherwise we'd expect the metabolism of test > aromatase > estradiol to have the stronger effect. In other words, it's unlikely to be entirely about oestrogenic activity.