The truth was, I didn't know. But I knew it would be seen as a failure if we didn't get an interview.

As a director and producer, I have made documentaries about some big businesses - like Google and Microsoft - and some big characters - like Donald Trump and Lord Sugar.

But Facebook is different. Mark Zuckerberg is only 27, and he's already had a movie made about him.

The Social Network told of his rise from Harvard dorm room to world domination. What more could we say in a documentary?

Well, for a start, the movie is out of date. It's based on a book published two years ago - and in the world of Facebook, that's ancient history.

And as Facebook prepares to float on the stock market, perhaps next year, the big question is whether it could possibly be worth the $100 billion that's being talked about.

That was our starting point: as a Money Programme production, Mark Zuckerberg: Inside Facebook looks at whether Facebook deserves those amazing valuations.

Of course, we also wanted to have a bit of fun, comparing reality with the movie.

We filmed at the real house that Zuckerberg and his friends rented in Silicon Valley: the one with the zip wire over the swimming pool (if you've seen the movie).

You'll see the New York journalist Jessi Hempel confirm in the programme that the poolside parties weren't pure Hollywood mythology.

The first she heard of Zuckerberg was when she got a call from a young guy with a lot of shouting and splashing in the background.

Today, it's journalists like me trying to reach Zuckerberg, not the other way round.

It's hard to make a film about a moving target, and Facebook doesn't decide what it's doing - in public at least - more than a couple of weeks ahead.

That makes planning filming trips rather tricky - especially when we needed to fit in with the busy schedule of our presenter, Emily Maitlis.

Emily Maitlis at the house once rented by Mark Zuckerberg and friends

But after endless changes, delays and rearrangements, Emily, my assistant producer Jo Hicks and I found ourselves with Mark Zuckerberg at Facebook HQ in Palo Alto, California for the interview we'd spent months negotiating for.

So how was he?

Well, he was polite, cheerful, sweaty (by his own admission, as he was fighting off a fever), and he talked fast, very fast. Which was good, as we had so much we wanted to ask him.

What struck me was that he talks just like any normal twenty-something.

Almost every answer seemed to head toward the conclusion "... so that's really cool" combined with a winning smile. It's not what you expect from someone running a business the size of Facebook - but the absence of the usual corporate clichés was very welcome.

Jo and I were filming the interview ourselves on three cameras.

Setting up was a huge rush as our PR minders only found a suitable room to film in a few minutes before he was ready to see us.

When it was over and he was whisked away by minders, I was almost too anxious to look back at the footage.

Had I done something hideous, like switching the camera off instead of on at the vital moment (it has been known)? Had we plugged in the microphones?

Back at the hotel, I gingerly played back the interview. There he was, in full colour, with sound.

Anything more seemed like a bonus. And actually there was more: Zuckerberg has given us a really good interview, which we use throughout the film.

So, yes, I have met Mark Zuckerberg.

Charles Miller is the producer of Mark Zuckerberg: Inside Facebook.

Comments made by writers on the BBC TV blog are their own opinions and not necessarily those of the BBC.