According to Lelouch's entry in Wikipedia, Julius Kingsley is Zero (Lelouch).
Akito The Exiled
After Suzaku brings Lelouch to Charles, he offers to hand him over on the condition he be inducted into the Knights of the Round, much to Lelouch's dismay. Charles agrees, and uses his Geass to alter Lelouch's mind. With this, Lelouch becomes the empire's slave, Julius Kingsley, wearing an eyepatch over his Geass.
Lelouch makes a few appearances in the miniseries, first seen in Suzaku's custody as he clutches his right eye while begging his friend for water, only to be silently turned down. In his second appearance upon arriving in St. Petersburg, Kingsley proudly declares that the Emperor has placed him in charge of all the Eastern front operational planning for Britannia's military.
In the third episode, Lelouch encounters Shin Hyuga Shaing and others for a meeting. In which he tries to arrest the others in his plan. Lelouch showcases a clip to create fear and havoc within the city. Later on, he plays chess along Hyuga, but starts hallucinating Kingsley and past memories from Rebellion. Later on Hyuga figures out that he was both Zero and Lelouch and calls his squad. Suzaku, in an attempt to defend the secret, kills most of the squad whilst Lelouch rips off his eye-patch. Eventually, both are captured, with Hyuga later declaring Kingsley executed and revealing that he is Zero.
This entry summarizes the episodes in Akito The Exiled where Julius Kingsley (Zero) is seen.
Also, Lelouch's character profile includes Julius Kingsley as one of his aliases.
Lulu, The Black Prince
11th Prince of Britannia
99th Emperor of Britannia
Charles zi Britannia (father)
Marianne vi Britannia (mother)
Nunnally vi Britannia (sister)
Rolo Lamperouge (adopted brother)
Clara Lamperouge (adopted sister)
With the third episode revealed, it is stated that Zero and Kingsley are the same person, and he is but a brainwashed Lelouch serving the Emperor of Britannia.
According to Julius Kingsley's entry in Code Geass Wikia,
A young man with a striking resemblance to Lelouch vi Britannia whose left eye is covered with an eye-patch for unknown reasons.
In episode 3 of Akito the Exiled, Julius was revealed to indeed be a brainwashed Lelouch who is completely loyal to the Emperor of Britannia. His eye-patch hides his Geass. There are multiple scenes throughout the OVA series that suggest his state is relatively unstable, with his original personality briefly resurfacing, as indicated by Kingsley muttering Nunnally's name, and even going so far as to calling Julius Kingsley another being all together.