According to US Weekly, Pippa Middleton's sister, 31, alongside Prince Harry's brother, also 31, greeted volunteers at Kensington Palace on Thursday.

Middleton wore a long red coat, with a waist belt highlighting her slim and svelte frame. Though it has been less than four months since the new mom gave birth to the royal heir, she looks as if she is back to her pre-baby shape.

With her trim figure, many wonder just how the royal has bounced back so quickly after pregnancy. The key to Middleton's fantastic frame?

US reported that a source told them that the Dutchess does yoga with an at-home trainer once a week.

Middleton also could have worked off those baby pounds by staying active and keeping busy at appearances. For the Poppy Day event, the royal couple rode aboard a 1960s-era Routemaster bus, and talked with actress, Barbara Windsor. They were also seen chatting with people from the Royal British Legion Poppy Day Appeal.

Reportedly, there were 2,000 uniformed personnel, veterans and supporters out and about at London tube and train stations, collecting donations and putting on military performances for the event.

London Poppy Day hoped to raise 1 million British pounds in a single day for the British Royal Legion. The major holiday also marked the end of World War I.

And this important event is only one of many more that the royal couple have coming up. Their social calendar has only just begun to heat up as the extended holiday season kicks off, according to the celebrity news magazine.

The royal pair are set to host a winter wonderland gala, featuring Taylor Swift, for homeless charity, Centrepoint on Nov. 26 . The twosome will also even will spend the Christmas and the Boxing Day holiday with the royal and Middleton families for baby George's first Christmas.

Happy to see that Middleton dropped the baby weight in no time, and is making more appearances? Tell us in a note below!