alicehoffmans:

I don’t even have a rudimentary knowledge of the Borgias, so you should probably ask someone else?

My impression is that there were rumors that they were; and that the two of them did have a close relationship, perhaps unusually close for siblings of the gentry in that era. Beyond that, I really don’t know, but I don’t think there’s ever been irrefutable “proof” of incest between the two of them. 

lucreceborgia said: hi! sorry to jump in, but yes! the borgia family is indeed involved in many rumors, especially lucrezia! she was accused of having an incestuous relationship with cesare, but there is no irrefutable evidence of anything! but there is proof of an affectionate and close relationship!

Thanks! That was my impression as well; I just didn’t want to say anything incorrect. I’ve never done any in-depth reading on them.