No, while similar there are enough difference between them, like cutie mark, eye color and by the panels it looks like their coat color is slightly different.
 
@Background Pony #D1B3  
We haven’t seen terri belle fighting yet, so we just can’t tell but considering tempest also has magic she will probably win.

@Background Pony #D1B3  

 
It will be interesting if the two warriors, the earth poniess Terri Belle and the unicornss Tempest Shadow, meet each other in battle. They can also be equal in magic use as Terri has to use a mysterious amulet while Tempest doesn’t have much finesse in her broken horn, just raw power and rudimensional control.
 
Maybe the two will have a common counterpart among the people of the pegasi sometime in the future? Commander Hurricane must then have a worthy heir somewhere in Equestria.

What does everypony think of this?
 
Terri Belle vs Tempest Shadow

< ( terri belle is not a cutesy wootsey snuggle wuggle cuddle bunny chubby cheek cutie pie. she’d be exposed and cast out as soon as she showed up, whereas you can subjugate their wills with your wumpy pumpfy kissie wootie cutie face and your— )
 
( okay, okay I get it! ) >

Well, we’ve seen plenty of examples of immortal or at least very long-lived rulers in this world before this. Hopefully we’ll see more of them in the future and get a few answers.

@Joshua  

 
There is current canon in the IDW comics with immortal royalty as seen in the arc “Cosmos” and other comic stories. In the FiM TV show, nothing about immortality - neither confirmed nor rejected. Moreover, it is possible to see that the two kings are not the same; The historical Thrace appeared to be somewhat more powerful in his physique than Diomedes, who has a different cutie mark. On Thrace you can see longer sidelines along the middle line while these are much shorter on Diomedes which appeared to be somewhat flimsy in his physique.
 
Cutie marks are not seen on Terri Belle, Blonni Di and Shining Light, but a comparison between the father and his daughter Swift Foot shows that cutie marks based on T-shaped masks in different variants may be the rule for the Thracians, especially for the royals. If the hypothesis that these mysterious masks are not protective equipment, but magical objects in which to project internal magic from earth ponies is correct - these must be important to the people to whom Swift Foot belongs.
 
Terri Belle knows her stuff like infiltration and espionage in Equestria, as she organizes the entire assignment for Swift Foot which was chosen simply because she was the only option, and knew how to deceive Twilight Sparkle with paperwork - which is not easy. The mission failed because her little sister is weak-hearted and because the Young 6 learned the importance of open and fair communication. If Terri Belle had taken Swift Foot’s place, Twilight would have been greatly embarrassed.
 
“Filika”? Very interesting name - and although Twilight had not heard of it, she is not the type to be deceived by official documents that cannot be falsified for fear of being discovered. So Terri Belle had probably stated the real location it is known to the authorities of Equestria. But without mentioning that there is currently a state called Thrace on a volcanic island. It is an Greek word that, ironically, can mean “friend”. It can have nautical significance, and the island is far out on the sea. The Thracians are probably far more similar to ancient Greek ponies than “barbaric” ponies would suggest - Thracia was located outside of ancient Greece in our world.

Definitely implied as a long line of heirs to the throne between the two. Enough small diffs to be different but keeping family traits.

@ImperfectXIII  
There we go, fixed.

@Joshua  
You mean “descendant”, not “ancestor”.

It would probably make sense if Diomedes was Thrace’s descendant. Then again, the idea of an immortal king is pretty awesome.