It was clear from the woman's tone and gesture that the label of "fat lady" was referring to the late stage of Meghan's pregnancy - that being a "fat lady" is something to be proud of. Bursting into a fit of laughter, Duchess jokingly replied: "I'll take that!"
The Mayhew was established in 1886 and the Queen became patron in 1974.
The dress also didn't stop Markle from petting the dogs in the animal shelter while she visited.
Meghan Markle visited her new patronage, the animal charity Mayhew, on Wednesday - where she met with staff, volunteers and beneficiaries.More news: British PM Theresa May's Brexit Deal Rejected By Massive Majority
Meghan has taken up the post of Patron to support the education and animal welfare work of Mayhew.
Kensington Palace posted more photos of her first visit to the center, too. The organization's goal is to better the lives of animals and people in communities they live in, both in London and internationally, through programs that work to reduce the number of animals in need including community and educational initiatives.More news: Kylie Jenner's Instagram record battered by an egg
Meghan, who is six months pregnant, showed off her large baby bump in a stylish figure-hugging dress by high street retailer H&M, with a coat by Armani, when she visited her new charity Mayhew.More news: Seeds just sprouted on the Moon for the first time in history
Later in the evening, Meghan completely changed up her look as she stepped out with husband Prince Harry for a charity performance by Cirque de Soleil.