Ty Tennant's role may not be all that big, but nevertheless it's essential for the story.
Another British addition to the cast of House of the Dragon: young actor Ty Tennant got a very important role in the sixth episode and will play the grown-up King Aegon. Not many people know that Ty Tennant is the son of the famous British actor David Tennant, though not biological, but adopted. Ty is the son of Georgia Tennant, David's current wife, from her previous relationship.
In the promo for the sixth episode, which follows a time-jump, the grown-up Aegon, played by Tennant Jr., can be seen fullу: the young blond prince, dressed in armor, is told by someone behind the scenes that he will become a king.
The appearance of Ty's character marks the increasing tension in the plot of House of the Dragon: very soon Aegon will have to fight for the throne with Rhaenyra, whom King Viserys himself called his heir. But Aegon and his mother, Viserys' wife Alicent, once Rhaenyra's former friend, have very different plans: it is he who is to take the Iron Throne. Aegon in episode six is supposed to be about 13 years old, and it's interesting that Ty Tennant is significantly older: he's 20 years old.
David Tennant himself has repeatedly admitted in the past that he would really like an opportunity to star in Game of Thrones. Unfortunately, the actor never managed to get a role in the iconic series, but his son will still get to know dragons up close. Perhaps Tennant Sr. did make his dream come true, at least by visiting his son on the set of House of the Dragon.
Ty Tennant is only 20 years old, but already has some pretty impressive roles under his belt. Fans loved him in Doom Patrol, however brief that stint was, and were utterly heartbroken upon learning that Ty's character isn't returning on Dead Boy Detectives series, with some even admitting that Ty's quitting the series "ruined" it for them. Ty, unfortunately, will not stay long on House of the Dragon: his role is limited to only one or two episodes. After that, we'll get a second time-jump and meet adult Aegon, who will be played by yet another actor.
It should be noted that time-jumps on the show are indeed serving an important purpose, explaining all the intricate backstory of the main characters before have them battling it out in a civil war. Consider the first few episodes as some sort of an extended prologue: time-jumps will stop after episode 8 and that's essentially when all the fun will begin.