Michelle Obama strayed from her tried and true designer rotation in the latest episode of her podcast, “IMO,” featuring Serena Williams . The former first lady — known for being an avid fan of Carolina Herrera, Michael Kors, Prabal Gurung and Jason Wu — donned a black viscose dress by Celine , embellished with a trail of gold buttons down the skirt. Online, the ready-to-wear design, priced at $6,600, is pictured with a halterneck. However, Obama is seen wearing the dress tank top style. Michelle Obama filming the latest episode of her podcast, “IMO,” with Serena Williams . Ashley Osborn Alongside her, Williams wore a chunky white cardigan layered over a steel blue draped minidress, cinched by a thin belt in the middle. The legendary tennis star’s blond braids were pulled off her face and fastened in rose buns on top of her head. Obama, similarly, tied her caramel-colored braids in two space buns behind her ears, leaving only a few curly strands tickling her cheeks.…