Meghan Markle took her fetus for a night on the town Tuesday -- hitting the famous Polo Bar restaurant for dinner with her pal Serena Williams ... and we've got the video.
Her Royal Highness had a busy day -- she flew into New York for her baby shower at The Mark Hotel earlier in the day ... where friends like Abigail Spencer and Jessica Mulroney helped celebrate the mom-to-be.
Afterward, it was off to Ralph Lauren's Polo Bar -- famous for its $20 "RRL Hot Dog" -- which comes with sauerkraut, sweet relish & mustard on a toasted brioche bun.
If she didn't have the dog, she missed out.
On the way out, 37-year-old Meghan strutted to her waiting SUV while clutching a fancy black Stella McCartney purse.
FYI, everything Meghan touches seems to sell out in minutes -- guessing royal fashion-aholics already snapped up the remaining stock.
Serena followed Meghan and got in the same SUV.
By the way, Serena and Meghan have been close for years -- they met at a Super Bowl party back in the day and grew so close, Meghan even invited the tennis legend to her wedding to Prince Harry.