He would know a few days in advance. From Nevill.
Her visits would have been sporadic and spontaneous. Partly depending on her condition.
So he would not know long term plans as there wasn't any.
All crap and bollocks from the Hippo. Pure speculation. You would have to have been making a fly on the wall documentary to have this level of detailed information of family life at WHF.
JB had an oedipus complex relationship with June but to hide their deep love of each other they pretended to be enemies and decided to bump of his father (as in the legend) along with the other family
members. They planned it together and would blame it on SC. Unfortunately the police shot June and JB took the rap.