I've just finished watching the Doctor Who Movie that they did in 1996. I was wondering does anyone have a Theory on how The 8th Doctor (Paul McGann) became the 9th Doctor ( Christopher Eccleston) ?

Yeah, maybe he regenerated.

Doesn't the first episode of the 'Russell T' first series allude to the regeneration having taken place very recently?

The Doctor catches himself in a mirror and makes some comments about it not coming out too bad (paraphrasing totally here).

One that was mentioned a while ago was that McGann was the one involved in the Last Great Time War and regenerated in CE due to what he had to do