SEE IT: Kate Middleton Debuts Shapely Arms in Royal Red Gown

The Duchess of Cambridge has discovered a secret many mothers have known for quite some time now: Carrying around a kid or two will help you tone those arms. PICS: Prince George and Princess Charlotte Land in Canada, Future King Isn't Too Impressed Kate Middleton, who is the mother to Prince George, 3, and Princess Charlotte, 1, flaunted her super-lean shape while attending a reception for political and civic leaders in Canada on Monday evening. (The 34-year-old, along with husband Prince William and their two children, are currently on a royal tour of the country.) The Daily Mail reports that Middleton turned heads in a Preen By Thornton Bregazzi sleeveless red gown, which is worth a whopping $1,298.30 (and probably sold out by now). She completed her look with the royal family’s diamond maple leaf brooch, "given to the late Queen Mother by her husband, King George VI, to mark the state visit to Canada in 1939." And it looks like Middleton was proud to show off all the heavy lifting she’s been doing thanks to the future king of England and his baby sister. PHOTOS: Prince George Steals the Spotlight at Trooping the Colour Parade See the royal’s latest red-hot look for yourself below: