Kate Middleton and Prince William prepare to meet staff and volunteers from the Royal British Legions London Poppy Day Appeal at Kensington Palace on November 7, 2013 Credit: Carl Court/AFP/Getty

What is Duchess Kate's secret?! With Prince William at her side, Kate Middleton greeted staff at volunteers at Kensington Palace in London on Thursday, Nov. 7 for London Poppy Day. Befitting the day's "poppy" theme, the new mum, 31, wore a long red coat that was belted at the waist and emphasized her svelte, slim frame -- which appears to be more or less back to its pre-baby shape less than four months after Middleton gave birth to son Prince George.

For the event, Kate and William, also 31, rode aboard a 1960s-era Routemaster bus and chatted with actress Barbara Windsor and folks from the Royal British Legion Poppy Day Appeal.

With 2,000 uniformed personnel, veterans and supporters out and about at London tube and train stations across London's mass transit network -- collecting donations and putting on military performances -- London Poppy Day hopes to raise 1 million British pounds in a single day for the British Royal Legion. The holiday also marks the end of World War I.

The royal couple's social calendar has only just begun to heat up as the extended holiday season kicks off: They're set to host a winter wonderland gala (featuring Taylor Swift!) for homeless charity Centrepoint Nov. 26 -- and they'll spend the Christmas and Boxing Day holiday with both the royal and Middleton families for baby George's very first Christmas.

As for Kate's enviable figure? A source tells Us she does yoga with an at-home trainer once a week.