While in the town of Ballymena, Kate was filmed greeting one of the locals, who was holding their five-month-old baby, when she made the remark.
"He’s a very sweet boy… He’s so diddly. Makes me very broody," Kate said.
The cute interaction between Kate and the infant called James occurred while the Duchess was visiting locals at Belfast’s Windsor Park Stadium.
Bending down to speak to the baby, Kate said: "Hi James! How old are you? Hello!"
She then turned to the boy’s father and said: "He's a very sweet little boy. How old is he?” to which the father replied, “five and a half months".
The touching moment was caught on camera, with the Duchess gushing over the infant, before she said goodbye to little James and continued on her way.
While there has been no official word from the palace that Kate and Wills want to have another bub, a royal insider recently hinted baby number four isn’t out of the question.
According to Us Weekly, the source said Kate “would love to have one more child” with Prince William, as they have loved watching their children engage with each other as they grow up.
"Painting, baking and building things are all activities they enjoy, and now that Louis’ a bit older, he gets involved too," the insider said.