Red hot mama!

Kate Middleton greeted staff and volunteers at London's Poppy Day charity appeal on Thursday, showing off her tiny waist in a long red L.K. Bennett coat, black opaque tights and black heels. She finished off her elegant ensemble with her signature wavy hair and polished makeup.

It's been less than four months since Prince George was born, but it sure looks like the Duchess of Cambridge has her pre-baby body back. So, what's her secret?

The 31-year-old has been an avid runner for years, so she continued her fitness routine after having the baby. “Kate stayed super-fit by running and hitting the gym. That helps in bouncing back,” a source told E! News.

Living at Kensington Palace also has its fitness perks. The new mom takes long walks on the property and also works out one-on-one with a personal trainer, according to E!‘s source.

Another big help in Kate's post-baby slim down? A healthy diet.

According to royal expert Kate Nicholl, the brunette beauty snacks on muesli bars and fruit smoothies made by her mom, Carole Middleton. Exercise, check, diet, check -- seems simple enough!

We think the Duchess looks better than ever, but what do you think of Kate's diet and exercise plan? Sound off below and click "Launch Gallery" to see Kate's post-pregnancy style!

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