During her visit, the Duchess was filmed getting up close and personal with rescue dogs, and she particularly loved a little Jack Russell named Minnie.
The duchess toured the charity's north-west London headquarters in Kensal Green to mark last week's announcement that she has become the organisation's patron.
Meghan rescued her dog Guy from a shelter in 2015 and she and Harry are believed to have adopted a second pup previous year.
"I'll take it", Meghan, the Duchess of Sussex, said Wednesday with a laugh after a woman, pointing to Meghan's bump, called her a "fat lady".
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Markle, 37, gamely held some of the charity's rescue dogs and petted others as she visited with staff and volunteers at Mayhew, which offers veterinary care and support for dogs and cats around the world.
In fact, her wedding makeup artist, Daniel Martin, told PEOPLE that Meghan isn't the biggest fan of a bold lip.
It is thought Meghan researched Mayhew on the internet before approaching the charity to learn more about its work, and made two private visits, the first in November, before her public tour.
Meghan waved as she walked into the centre to greet those who work at the charity, which aims to improve the lives of animals and people in the city.
The Duchess of Sussex paired a $35 H&M cream maternity dress with a cashmere coat by Armani for her visit to Mayhew.
And it looks like the Duchess of Sussex makes the pawfect Patron for the charity after she was seen cuddling one of the puppies and cradling it on her blossoming baby bump.