New Tommen Baratheon?

It looks like we might have a new actor playing Tommen Baratheon, the younger brother of King Joffrey Baratheon. 

In the previous seasons Tommen was played by the young actor Callum Wharry, last seen in Season two's famous episode Blackwater.  It now looks as though the role of Tommen Baratheon will be taken over by Dean-Charles Chapman. 

Now here's the real catch, Dean-Charles Chapman has previously appeared in Game of Thrones as Martyn Lannister, one of the squires that was killed by the Karstarks in the Riverrun dungeons in Season 3.

I personally thought Callum Wharry was great as Tommen.  He was young and had a very innocent look to him, which really captured the essence of Tommen.  I know Tommen is going to get more screen time in Season 4, or at least I assume he will, so HBO wanted a more experienced actor to take the reins of Tommen.  But the fact that they got someone so much older is kind of surprising to me.