Newsround's Lizo reported from the Luna Lovegood open casting in London.
Thousands of girls turned up to be seen, and some of them even camped overnight to be first in the queue.
Here he reports on what is was like for those patiently waiting in line to be seen by the Harry Potter casting director.
Wow. What a day! This time last week, I was planning what stories I'd be chasing up over the next few days. A piece of paper was stuck to my computer screen and top of the list was 'check up on Luna casting'.
Like everyone else, I was expecting to hear a name sometime in January. I had no idea that in seven days time, I'd be walking down a queue of teenagers more than a mile long - all hoping to be cast as Luna Lovegood.
The queue snaked around the block
After a lot, and I mean a lot of phone calls and planning, we broke the news about the open casting on Newsround on Tuesday. We hoped that lots of people would show up, but of course you never know.
But when I walked out of the tube station at 8.30am on Saturday, the first thing I saw was a queue stretching out of sight into the distance.
Undoubtedly the most amazing part of the day was meeting so many Harry Potter fans. Thousands of them. Despite the fact that people were queuing for hours on end the atmosphere was wonderfully friendly.
Cheerful and friendly
We chatted to as many girls in the queue as possible. They were there from across the UK. As well as America!
Despite all we'd said about girls having to be from the UK and Ireland, I still met one woman who'd flown in from Texas in America with her grand daughter.
Parents should naturally get a mention. Many of them cheerfully admitted that all they'd heard since Tuesday was Luna this, Luna that, Luna everything!
And daughters who on a weekend couldn't normally be coaxed out of bed before midday, were begging to be driven down to London at 4am from far flung parts of the country.
And they chatted to other parents in line, swapping stories of the dire retribution their daughters had promised if they weren't allowed to go to the casting.
Posing for snaps
Girls fill out their details on forms
At the same time the girls were loving the attention, posing for the snappers. Screaming for the cameras and generally having a brilliant time.
Remarkably, the weather stayed dry until the last girls went in at around 4.45pm. At that moment it started raining. Had it happened earlier, it would have more than dampened people's enthusiasm.
Knowing that the odds were against them, didn't seem to matter either. Just because there were more than 15,000 other girls in the queue didn't seem to matter. They really believed in themselves for the part. And no one was going to change their minds.
Except for a few people who were upset that they didn't get further than the day's casting call, most girls seemed to enjoy themselves immensely whether they were shortlisted or not.
And a few were all grins, getting through the casting and even being filmed reading a scene between Luna and Harry.
One girl will be doing that for real soon, and like everyone else, we can't wait to find out who it will be.