The doting mum delighted fans with a new photo of His Royal Cuteness on Facebook and captioned it: "Time is flying, can't believe my sweet Nicolas is 9 months!"
The royal baby, who is currently seventh-in-line to the Swedish throne, was pictured gazing skywards with his bright blue eyes, while he held out his hands mid-pose.
It's been just a couple of months since Madeleine shared photos of her little boy, but royal fans were quick to comment on how much bigger – and even more handsome – Nicolas is.
In January, the Swedish beauty and her husband Chris O'Neill ventured on an exotic getaway to the Maldives, in search of some winter sun. The couple brought Nicolas and older sister Princess Leonore, who just turned two, on the holiday.
Madeleine, 33, cradled her baby boy to her chest as she posed for one photo against the idyllic backdrop of a crystal blue sea. In another, Madeleine's Facebook followers were able to catch another glimpse at Nicolas flashing a gummy smile at the camera.
The young royal was born on 15 June in Madeleine's native Sweden. At the time press officer Margareta Thorgren revealed that the baby weighed 3,080 grams, measured 49 centimetres and had his father Chris' chin.
Businessman Chris also revealed that the first meeting between Nicolas and his big sister Leonore had gone well – and that "Leonore thought [Nicolas] was a doll".
Last year the family-of-four relocated to London, a city Madeleine has previously lived in, for Chris' job. The princess has said that she feels she can be more "anonymous" in the English capital.
Despite having grown up in the public life, Madeleine admitted she still doesn't "like being the centre of attention".
"I've had this all my life. One would think, and maybe expect, that I'd be comfortable in front of people, photographers and journalists who ask questions," she said during an appearance on local show Skavlan. "But I'm really not, I'm quite shy."
Madeleine still makes frequent trips back to Sweden to carry out royal engagements and spend time with her family. Earlier this month she was in Stockholm to meet the latest arrival to the family, her nephew Prince Oscar, Crown Princess Victoria's second child.