The 34-year-old Scots superstar is doing for beards in Episode III: Revenge Of The Sith what Princess Leia did for bagel hairdos in the original Star Wars 28 years ago.
'It's not a big, fluffy beard really, more like a goatee,' laughs McGregor, who was required to sport fuller facial growth in order to smooth the transition of his young Obi Wan Kenobi in the recent Star Wars prequels to the OAP version played by the late Alec Guinness in the original trilogy.
'It's been more important this time around than in other films to get an Alec Guinness look and feel. Initially there was talk of a wig as well, but I fought it. My natural hair is quite like Alec's, so I got away with just an Alec Guinness-y haircut.
'It's no longer a mullet, which I sported beautifully in Episode II. I've passed that on to Hayden (Christensen, who plays Anakin Skywalker) - he now carries the mullet flame though Episode III.'
The real hairy moments for Ewan in Episode III came from the emphasis placed on action - something that will no doubt please all those disappointed with the previous two prequels.
Fans the world over are drooling with anticipation of the epic battle in which they will see Anakin beaten by Obi Wan, only for Vader to rise from his burnt remains.
'The third film is by far the most challenging,' says McGregor, who went though weeks of fight training and rehearsals in order to act out the film's climactic lightsaber battle.
'Hayden and I really go at each other for such a bloody long time. But, of course, in the end I win.'
Ewan was a sprightly 28-year-old when he first picked up his lightsaber for The Phantom Menace and it seems all those movies since, not to mention his recent trans-world motorcycle trip with best pal Charley Boorman, have taken their toll.
'Yes, it was very slow going - not that I'm a bit older than when I filmed Episode I,' admits the busy father-of-two. 'For that film, I'd fight all day long, I didn't care. I was like, "Let's do more." Whereas now it's like, "Okay guys, I think that's it, I've reached my limit."
'I really noticed how much my stamina had decreased in that respect. But it was a slow process, and I think that was the best way to approach it, because we weren't going to get all of them done at once.'
Ewan makes no attempt to distance himself from the over-obsessed thirty-somethings who grew up with Star Wars and still can't resist a trip back to their childhood and to that galaxy far, far way.
For almost a decade now he has been living that same childhood dream, even if he has often been critical of the prequels to the original Star Wars movie that thrilled and captivated him as a wide-eyed seven-year-old back in his Scottish hometown of Crieff, Scotland.
Ewan admits to feeling more than a little sad at completing his Jedi commitments. He even confesses to getting 'choked up' during a scene with dustbin-like robot R2D2. 'He made me remember what it was like to be seven and watching those films,' he says. 'It was quite a moment.'
Ever so slightly misty-eyed, he continues, 'I loved Star Wars when I was a kid. I remember I wanted to be Luke Skywalker, with my own lightsaber. I still like to watch the older versions now.
'I often said it was for research, but I haven't got that excuse now. The truth is I just like watching the movies. To be appearing in the more recent films has just been fantastic. It's been a fun ride and I have met plenty of good friends but, like any ride, it has to end.'
