Mad Men actress January Jones wore a black jumpsuit without underwear Credit: Theo Wargo/NBC/NBCU Photo Bank

Oh, Betty! January Jones turned up the heat as she left her undergarments at home during an appearance on The Tonight Show with Jimmy Fallon on Friday, March 28.

The Mad Men actress, 36, wore a revealing, yet classy, black jumpsuit by Zuhair Murad for the visit with matching heels. The plunging neckline ensemble showed off major skin with cut-out detail placed strategically down her leg. To top it off, Jones kept her makeup simple with a touch of light blue color.

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Earlier in the day, Jones stepped up her fashion game once again in an '80s-inspired look. The X-Men star was photographed outside her hotel in NYC wearing an edgy white blazer with a black t-shirt and J Brand "Genevieve" jeans. She completed the look with a bold red lip and bee-hive hairstyle.

Jones and her fellow AMC costars are currently in NYC for the show's upfront presentation. On March 27, she shared a stunning selfie in her hotel room. "Objects in a @tomford mirror are prettier than they appear. Thanks @hungvanngo @rebekahforecast," she wrote.

Tell Us: What do you think of January Jones' revealing black jumpsuit? Tweet with @UsWeekly using #stylebyUs!