In the previous episode of The CW’s Charmed, the Charmed Ones tried to communicate with their mother through a spirit board, which warned them not to trust their whitelighter, Harry.
The Book of Shadows turned to a truth serum, and the girls planned to use it before deciding whether to trust Harry.
Since the truth serum was a bust, Mel asked the spirit board questions only Marisol would’ve known, and it convinced her and Maggie they were speaking with their mother.
While they discussed whether to trust the spirit board or not, they came up with a code name for him: Meghan Markle.