Meghan Markle is recalling a horrifying incident ... where she learned baby Archie's nursery caught fire while they were away.
The Duchess of Sussex opened up about the incident for the first time on the premiere of her podcast, "Archetypes" -- telling Serena Williams in 2019 that her son was 4 months old when they took him to South Africa.
She says they dropped their son off at a housing unit before going to give a speech nearby ... and when she was done, Meghan learned a fire had broken out in Archie's room.
After racing back, Meghan found Archie unharmed -- his nanny took him out of the room while she went to go get a snack ... after they walked out, a heater in the room caught fire.
What's worse -- after the close call, she was forced to leave Archie behind again to go to another engagement, despite asking to cancel the event.