This is just speculation on my own part from observations of the series. this will most likely be dis-proven once the episode has been released and there is an official statement on my observations

Julius is a clone.

In R2 we find out that Suzaku brought Lelouch's to Charles where Charles then used his Geass to alter Lelouch's memories. Lelouch's Geass (now out of controlled) is also shown to be sealed and then unsealed thank inpart to C.C. Julius being a clone with out of control Geass would explain his eye-patch (as after R2 Starts C.C has developed the contact lenses to block the Geass).

Also all of Lelouch's friends has their memories altered. had he been missing for a long time this would take 2 Memory Alterations, one to make them forget Lelouch ever existed and another to reinsert him (and Rolo) into their lives for when they were trying to draw out C.C and the Black Knights.

As for how i suspect the Order, remember the Order has been working on trying to duplicate Geass as i don't think V.V made contracts with every one of them. there are children with an ability similar to Lelouch's which could indicate that the Order attempted to clone Lelouch's Geass by cloning him (possible fail-safe incase if they could not activate the sword, world wide Lelouch Geass Order to strip individuality by becoming the same person).

By Akito of the Exiled Suzaku should also be an affiliate member of the Order due to his position with the emperor (and later his knowledge of the Sword of Akasha). Suzaku's disgust for Julius would be because he looks like Lelouch and forces Suzaku to remember him.

Finally their eye(s)

Notice how Julius's is not the same purple...however this might be a production/lighting thing however you will notice Julius's hair at the front is also longer while even in R2 Lelouch's doesn't change all that much. however likewise could be a production thing

In episode 3 of the OVA series it's revealed that Julius Kingsley is infact a brainwashed Lelouch. the brainwashing however is somewhat unstable as when Julius is seen on the train cluching his eye this is a sign that the brainwashing hasn't fully worked and "Lelouch" is trying to come back. he reappears briefly later on showing also that his Geass has yet to be sealed as it is at the start of R2