House of the Dragon has certainly changed a few things from the book. Some of these changes are easy to explain and mean nothing. Others are a little more crucial to the plot.
Fire & Blood isn’t written as a traditional novel, though. It’s a story written out by a Grand Maester, with him telling the story of the Targaryen reign via the reports of three people. Nothing is actually set in stone, as sometimes, the accounts of the three men differ.
This does allow a little more creative freedom for the show. There are a few things that don’t work quite as well, but there are other parts that we gain a little more information about. One of those is the lineage of Alyn and Addam of Hull.
Addam of Hull may be the grandson of Corlys in Fire & Blood
In Fire & Blood, the paternity of Alyn and Addam of Hull is never confirmed. This is mostly because nobody officially claimed them as his son. However, there are connections to House Velaryion.
Alyn and Addam’s mother claims that the two are sons of Ser Laenor Velaryion. This is disputed by people in the book due to the knowledge that Laenor preferred the company of men. It’s partly why there is such a strong suspicion that Rhaenyra’s three elder sons are sons of Harwin Strong rather than Laenor.
Of course, gay men can have children. We all know that. It’s just that people don’t really believe that Laenor is the father.
Corlys is the suspicion in Fire & Blood and confirmed in House of the Dragon
Instead, many believe that Corlys Velaryion is the father of the two boys. They say that Corly was dismissive of them and kept them away from Dragonstone because of his wife Rhaenys. It was claimed that she had a temper, and it was better for the boys that they remain far away from her. After her death and the sowing of the seeds, things started to change. They were legitimized, although still never as Corlys’s sons.
In the TV series, that has changed. Corlys has been confirmed as the father of the two. Rhaenys points out that she knows Alyn of Hull is her husbands son from an affair, but she doesn’t put the blame on Alyn and treats him kindly in the street. We don’t get an interaction with Addam, but she would have likely done the same.
Addam and Alyn know that Corlys is their father in House of the Dragon, while they believe Laenor is their father in Fire & Blood. This change likely won’t mean much, although it does bring up some questions about Addam riding a dragon. Corlys’s family isn’t one of dragonriders, so could it be a hint that Corlys is covering for Laenor? Probably not. Seasmoke chose Addam, and it’s likely the connection to Laenor, as it seems like the dragons respond to lineage but not in the way the Targaryens have always believed.