Karen Gillan and Matt Smith Karen Gillan and Matt Smith

The Doctor Who panel at Comic-Con offered the opportunity for fans to get a taste of what's to come when the show returns to BBC America on Saturday, Aug. 27 at 9/8c.

Before debuting the show's new trailer — which teases the returning episode "Let's Kill Hitler," among others — series stars Matt Smith and Karen Gillan gave a few behind-the-scenes insights into what it's like to play the time-travelling Doctor and his companion.

PHOTOS: Check out the stars at Comic-Con 2011

River Song's Secret Song and Dance

The surprising revelation that River Song (Alex Kingston) is actually Amy (Gillan) and Rory's (Arthur Darvill) backwards, time-travelling daughter even shocked the usually all-knowing Doctor — both on the show and in real life.

"We had a dummy ending on the actual script," Gillan explained. "We had the read-through and then after the read-through, [showrunner] Steven Moffat took us outside — me and Matt and Arthur — and he showed us the real ending. We just started running up and down the corridor! Only Alex knew [before that day]. My mom's quite excited that she's Alex Kingston's grandmother. "

"No spoilers from River Song," confirmed Smith. "Steven gave her more power. How can you give River Song more power [than The Doctor]?"

The secret-keeping continues on set, however, with Gillan knowing information about Amy that Moffat only told her. "My secret, I've still got," she teased. "You [Matt] still don't know it. It's so good! I feel really powerful right now. This never happens." "She won't tell me," Smith groused.

Torchwood's John Barrowman teases Doctor Who return

The TARDIS and the Time Lord

Smith revealed that he actually knows how to "fly" the TARDIS and that he's not just pulling levers randomly. "Can you believe when I turned up on my first day, they gave me a manual?" he said. "I taught Karen how to fly it. We spend hours just fiddling around.

"But if you look at the takes when I'm taking off and landing, it's always the same thing. There's a gear, clink back the big lever with lights and then the handbrake. And then there's a lab and a navigation system where he types in where he wants to go. The TARDIS never gets boring."

The time machine/spacecraft has survived a number of adventures on the show, but it also endures rough treatment on a daily basis, along with the Doctor's other signature device, the sonic screwdriver. "There's this great box and there are five sonic screwdrivers in there, and I break one a day," said Smith. "I'm always flying around, I'm really clumsy. And the TARDIS, there are always bits of it coming off in my hands."

Elisabeth Sladen, Doctor Who's Sarah Jane Smith, dies at 63

The Dream Lord and the Doctor's Dark Side

During the last season, fans glimpsed a manifestation of the Doctor's sadistic side called the Dream Lord (Toby Jones). Smith told the fans that he'd love to revisit that side of his character. "I'd love to bring him back," Smith said. "I'd love to see him with a big, huge army behind him. I think the idea of the Doctor's alter ego really presenting the Doctor a problem is a such an interesting one."

The possibility of a dark side doesn't have to be embodied by Jones though. In the last episode, "A Good Man Goes to War," the Doctor's hero status is challenged when it's revealed that at least one group of people interpret Doctor to mean "mighty warrior."

"I think there's a lot of blood on the Doctor's hands," Smith said. "I actually think that's why he's so bright and bubbly and effervescent and mad because he has to keep going, he has to keep moving, he has to keep traveling, he has to keep saving people, making jokes — because if he didn't, if he stopped, if he sat down, he'd have to contemplate losing the Roses, losing the Sarah Janes, losing all these people and letting them go. I think that's a very interesting area to explore."

Added Gillan: "I think in Episode 10 we see a bit of the dark side. Rule No. 1: The Doctor lies. That's going to be explored."

Matt Smith, Time Lord Stylist

Every Time Lord regeneration not only brings a new actor and face to the character, but also a new signature wardrobe. In the case of the 11th Doctor, Smith was the one who defined his now iconic style.

"We were looking for the costume, which is a huge decision," producer Beth Willis said. "Matt pulled the tweed jacket out of his bag and said, 'I think I should wear this.' And then he pulled the bowtie out of his bag, and we all went, "No!!" ... He put the bowtie on, and it just clicked. That was Matt. He came up with it all. So if he thinks a hat will work, it's worth a try."

That line of thinking led to the Doctor donning a fez, which didn't exactly match his tweed ensemble, but captured the fans' imaginations. "It's all a testament to Moffatt I think for having the ingenuity to be very clever," said Smith. "What's groovy about all this is that actually it's me bleating on about wanting to wear a hat. So he gave me the most stupid hat he could. It's actually him that makes fezzes cool."

Gillan pointed out, "It's only on screen for a really short period of time." "Because River blows it up. That annoyed me," said Smith. "But now it's all about the Stetson."

To check out what other possible head coverings the Doctor may fancy next, watch the trailer that debuted at Comic-Con for the upcoming Doctor Who episodes: