By Nick Dermody
BBC Wales news website
Christmas comes once a year, except in Cardiff, where it has already been and gone.
Cardiff's shopping area looked like Christmas in July
Back in July, shoppers in the city centre found themselves walking past a giant Christmas tree, a late-night festive market and Santa lookalikes.
It was as if the Welsh capital had somehow been flung into a different dimension. And in a way, it had been.
Perhaps thanks to the Tardis, the city was the backdrop for the Doctor Who special to be screened on Christmas
The Hayes shopping area of the city has played its part in another climactic galactic tale of the changeling Timelord and his earthly adventures.
Over two nights, the BBC Wales team which makes the show transformed one of the busiest areas of Cardiff into a tinsel and snow-filled location.
Robot Santas turn Christmas shopping into a deadly day out
They even borrowed the council's own Christmas lights to do it.
Producer Phil Collinson said: "The main problem was trying to find places that did not have leaves on the trees. We tried to be quite careful about that.
"We filmed on The Hayes, which wasn't so bad because it wasn't the greenest part of Cardiff.
"The people in the streets are so proud that this show is made here. It does make it easier for us.
"We have closed the main street for a whole evening. In any other place they would be shaking their fists as us, but in Cardiff, its 'okay, go ahead'.
A typical episode takes around two-and-a-half weeks to film, he said.
"We've had hordes of people turning up to watch. There is always a bang or a flash or a guy in a green suit to watch."
The seasonal episode, called The Christmas Invasion, was scripted by the series' Swansea-born executive producer Russell T Davies.
Other scenes were filmed on a London estate
He said the one-hour special would maintain the show's reputation for being frightening, even though it was going out at 1900 GMT, prime time family viewing in households across the UK.
"It's scary," he said. "That's why we can't show it after the Queen (the Queen's speech), but it's still good fun."
A team of writers had turns producing scripts for the first series, screened over the summer, and scenes for the second series - starring Scottish actor David Tennant in the role of the doctor - are already in the can.
But the seasonal special was a treat Davies reserved for himself.
He said: "I would never have let someone else write the Christmas episode - I have been dying to write a Christmas episode all my life."
As the programme's credits roll, digital television viewers can take an interactive TV challenge by pressing the red button.
A mini episode, Attack of the Graske, gives the audience an opportunity to fly the Tardis.
An exhibition dedicated to Doctor Who is going to be launched in Cardiff Bay on 22 December to help celebrate Cardiff's golden jubilee as the capital of Wales.