The pair, as well as Alexandra Burke, are early favourites to win the competition given their past dance experience.
But the pop star trio confess they're worried about living up to the hype.
"We’re used to being disciplined to a certain degree, but I think there is an expectation people will have, and I feel like Aston and I are both terrified!" Mollie admitted this week.
She added: "It’s a whole new world for both of us and, we don’t want to look like complete wallies!
"There's so much for us to learn and so it's lucky we have performance experience as it’s a whole new world of dance."
Meanwhile, for Alexandra and Aston, the competition is a bit more personal.
Alex beat Aston to win The X Factor in 2008 when he was a part of JLS.
Joking that Strictly would be "round two" for both of them, Aston praised his rival: "I love Alex. She’s a proper firehouse when it comes to dance especially.
"So much charisma and talent. She’s an incredible woman, I can’t wait to see everyone dance but Alex is going to be amazing."
Last night saw the celebs get their pro partners as the new series kicked off.
Mollie King was paired up with AJ Pritchard, Aston Merrygold is with Janette Manrara and Alexandra Burke is dancing with Gorka Marquez.
All the couples now face two weeks of intense training before their very first dances.
Strictly Come Dancing goes live on Saturday, September 23.