Although this fanfic was written long ago, it became popular when The Force Awakens was released because Kylo Ren was obviously not a cyborg. But, the author added a new foreword saying that the theory couldn't be denied because Leia could still have a secret cyborg child.
The basic premise was that Leia fell for C-3PO and they even secretly had romantic relationship (in the new foreword, the author also wrote that it was possible Han Solo left Leia because he discovered this relationship). The fanfic also used behind-the-scene pics depicting the relationship:
Can you please identify this fanfic?