Speaking to What's on TV, the sci-fi drama's new companion revealed that Time Lord co-star Smith made her feel comfortable in the audition.
Coleman recalled: "Matt was in the audition with me and made me feel like we were in it together. He says we're going to have the best time ever!"
Unveiled to the public a fortnight ago, the 25-year-old will make her debut during this year's Doctor Who Christmas special.
Smith has continually paid tribute to Amy Pond actress Karen Gillan, who Coleman will replace.
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Watch former Time Lord David Tennant talking to Digital Spy about Coleman's casting below: