Oh wow...yea that's a big fukking deal.They cut Jaehaerys II from the family tree. In Game of Thrones, Maester Aemon says the Mad King is the son of Egg, meaning Jaehaerys II didn't exist as a king. GRRM apparently let the new showrunners know that he hated this change and wanted them to somehow fix it.
'House of the Dragon' showrunners say George R.R. Martin requested 3 details from his books be included in the series
Miguel Sapochnik said the author had a "bee in his bonnet" over a Targaryen line of succession detail left out of HBO's "Game of Thrones" adaptation.www.insider.com
I'm at Jaehaerys reign right now in the books(The OLD KING).