The Duke and Duchess of Cambridge released their first official family photos with Prince George on Monday, and already Kate Middleton's purple-magenta maternity dress from Séraphine has sold out. The "Kate effect" is quite influential, and Yahoo! Shine reports that Middleton is making more than just a fashion statement with her post-baby style.

Just a day after giving birth to Prince George, the Duchess stepped back into the spotlight to show off her beautiful son to the world, letting her post-baby bump proudly show in a classic polka-dot Séraphine maternity dress. Predictably, some tabloids jumped on her for not hiding her belly, but overall the reaction was extremely positive, as millions of fans were inspired to embrace their own bodies.

For the first official family photos, Middleton and Prince William kept it simple in more ways than one. Instead of going along with royal tradition and hiring a professional photographer, the couple opted for Michael Middleton to take the casual pictures as the family lounged in the Middleton manor garden with their son and family dogs. The Duchess kept things classic yet casual with her $79 maternity dress.

"She's really showing she's not trying to be like a celebrity. She isn't trying to give an image meant to impress or pretend she's already got a flat stomach," Cecile Reinaud, founder and creative director of U.K.-based maternity label Séraphine, told Yahoo! Shine. "She's sending a very nice message to new moms. A big thumbs-up to her." Reinaud added that "two months" is the time it takes the average new mom to return to their post-baby body.

"If she likes something, she likes something. It's a refreshing approach, rather than having to have the most expensive things," said Reinaud. "There's a lot of self-confidence in that." 

Celebrity news and fashion sites have praised the royal couple for taking relaxed, easy-going photos for their first official portraits with Prince George, as after all, the Duchess wanted her son to be in a "natural and relaxed environment" for the photographs, as a source revealed to the Mirror. 

"Yet again, it was William and Kate saying they're doing things their way," CNN royal contributor Victoria Arbiter told Yahoo! Shine. "It's very clear where their priorities are: on each other and on their baby and their family."