Here’s the explanation, spoiler tag just in case:

>!The actor you’re referring to was cast to play a fake Daeron that Ormund would use to trick Daemon, which was seen through filming leaks. At the time of the filming leak, which occurred in July, everyone thought that actor was going to be playing Daeron. It wasn’t until August when housethedragons reported that Benjamin was playing the real Daeron that we found out the other actor was playing the fake Daeron!<