Lore:Ariella Septim

Crown Princess Ariella Septim (3E 374 – ???)  was child of Emperor Uriel Septim VII, and heir apparent to the Dragon Throne and the Septim Dynasty as of 3E 389. 

History
Heir to the Empire
During  , Ariella attended Mid Year's festival  in the Emperor's banquet hall some months before the Imperial Simulacrum began. The ghost of Ria Silmane would retroactively declare that the event was where evil took form in her master, the Imperial Battlemage of Tamriel, Jagar Tharn;  which holds at least some truth, it was here where General Talin Warhaft would regale to the Princess, Ariella Septim, about a time in his youth when a friend of his, Marten the Blade, used a spell of illusion to change his own appearance into that of another to trick a group of bandits into thinking Marten was their leader. It was this anecdote that inspired Tharn to do something similar... To remove his Emperor, whom he was terribly jealous of, and take his place. While ruffling through possibilities in his mind, Tharn knew that he could not simply murder Uriel Septim VII, for in that case, Princess Ariella Septim would ascend to the throne. Such a scenario was unacceptable to Tharn, who would only change masters, and would be even more ashamed to serve a woman. 

On Hearthfire 1 3E 389,  when Jagar Tharn enacted his conspiracy to take the place of his Emperor, Jagar had cast a seal spell on the floor, trapping Uriel VII and his Imperial Guard within a magical barrier of fire. Then did Tharn lay out his scheme to his royal adversary; to steal the visage of the living Emperor of Tamriel, and transport the true Uriel VII to a dimension where time passed more slowly, and when Uriel VII would eventually die, several generations would have grown up on Tamriel, with the glorious reign of "Uriel Septim VII" lying centuries in the past. Tharn assured the Emperor that he would take care of everything, including his precious child Ariella, who Tharn believed would "certainly understand" the value of fostering "family" alliances.  Indicating that Tharn planned on bedding the girl, possibly to create an heir, it's unknown if a child was ever borne of this threatened union.

Fate
Following these events, Ariella Septim never made a reappearance in written record. It's possible Ariella was dispatched with the Emperor's other children to various prisons disguised as schools during the Imperial Simulacrum,  and/or got replaced with a doppelganger, like her brothers were rumored to have been. 

By 3E 427, Geldall Septim was understood to be the Crown Prince and heir apparent to the Dragon Throne.  In later history, circa 3E 433, the Oblivion Crisis was set in motion where all known heirs of Uriel Septim VII were assassinated by the Mythic Dawn cult, with the exception of Uriel's secret son: a Priest of Akatosh named Martin Septim. 

Ariella Septim's status following these affairs ultimately remains unknown.

Notes


A maternal connection to Caula Voria for Ariella has not been spelled out. Ariella's heir apparent status indicates she is of legitimate birth, and Uriel is made out to have married only once per  A Life of Uriel Septim VII. It is a reasonable assumption to believe Caula Voria is the mother. 
Evidently, Bethesda did not know about Ariella's existence, given her total exclusion from all later products and materials.
One Morrowind developer said he said he had no idea in regards to her existence. 

References