Landing the part of Rose Tyler, the latest in a long line of time-travelling companions for the Doctor,
meant more to Billie Piper than anything in her career to date - including seeing her debut single top the charts.
"When that happened, I was in the midst of this mad pop frenzy and I didn't really have time to enjoy the
moment," recalls the pop star-turned-actress or actress-turned-pop star-turned-actress, as she would prefer.
"It's only on reflection that I can think how great it was, but at the time I couldn't feel it. It all happened
very quickly - I was only 15 and completely numb to that success, which is a shame.
"But the thing about acting is you have to be living the moment all the time, so you can enjoy it all the
time. I'm just happy to be feeling it this time round."
Still only 22, Billie has packed a lot into her life, including pop stardom and marriage to media mogul Chris
Evans, but she now feels she is finally doing what she was born to do - act.
"As a child, I always wanted to be an actor and I studied drama and did workshops when I was growing up in
Swindon," she says.
"I didn't just want it to be my hobby, I wanted it to be my life and to throw myself into it completely, so
I got a scholarship with the Sylvia Young Theatre School in London.
"It was always my mission to be an actor - I just got sidetracked somewhere along the line!"
Billie was asked to do a demo-tape for a new record label keen to find a new young female solo artist and,
as she recalls, "it just snowballed from there".
"I did it because I love music," she says. "I was never really that confident as a singer but I saw it as
a stepping stone and hoped that it would open doors for me in the future as an actress.
"I know there have been times when the whole pop thing has gone against me in terms of getting roles, but
I also knew I would just have to apply myself."
To that end, Billie went to Los Angeles to re-start her acting studies in relative anonymity, then came home
and began auditioning.
"The main reason I got parts was because I always considered myself to be an actress and it was only news
to everybody else. So I think it was my passion and conviction that got me my first couple of jobs," she says.
A role in the BBC's contemporary version of Chaucer's Canterbury Tales in 2003, opposite TV heavyweights James
Nesbitt and Dennis Waterman, made people sit up and take note of Billie's talent.
And when it came to trying to land the part of Rose in Doctor Who, she had an ace up her sleeve.
"I had a first audition and was then called back to read opposite Christopher (Eccleston) so the producers
could check out the chemistry between us.
"That was really quite scary, but I'd met Christopher before because we were going to be partnered up to do
another TV drama.
"Nothing ever came of that project, but at least we'd been out for a drink before and enjoyed each other's
company, so that definitely helped."
Billie sees Rose as more of an equal to the Doctor than his previous companions.
"The new series keeps the essence of the old Doctor Who, but one of the ways it has updated it is in the relationship
between the Doctor and Rose.
"I think they're on a par with one another, more like partners, and the audience sees everything through Rose's
eyes," explains Billie.
"She's human, the Doctor's an alien, and she's experiencing all these alien situations throughout the series.
At times, the whole thing is slightly overwhelming for her, but she can cope with it and match the Doctor.
"He is constantly challenging her, trying to broaden her horizons, and she's trying to show him how to be
more in touch with human emotions.
"The series is a great balance between science fiction, which can be a bit detached, and real, genuine emotions.
I don't think I would have done it if it was strictly sci-fi, as much as I've enjoyed being chased by monsters!
"I get my biggest buzz from working opposite Christopher when Rose and the Doctor are having 'domestic' kind
of conversations. But the creativity of the plots and their characters, the sets and the whole look of the series is amazing."
Billie admits that she sees a younger version of herself in Rose, especially the way she relies on her instincts
"She's only 19, and when you're that age you don't tend to analyse things as much, you tend not to think so
much about the consequences of your actions.
"That's what I like about Rose - everything about the Doctor's world is so brand new to her, and she's relying
on her instincts all the time and I love that."
Billie adds: "If Rose had been older she might not have gone off in the first place with this strange man
who calls himself the Doctor and abandoned the life she knows.
"But when we first see her she's so bored and looking for excitement. She feels trapped and doesn't want the
kind of mundane life she's living. But then she meets this guy who totally shakes up her world."