"Although Kate has done her best to offer Meghan help and guidance as she adjusts to life as a duchess, Meghan has made it clear she wants to write her own rule book," an insider spilled to the US tabloid.
"Doria is telling Meghan to stay strong and not lose sight of who she is. But Carole is reminding Kate that she's the one who is going to be Queen."
"They're trying their best to keep things civil," adds the source, "but this could be the beginning of an all-out war!"
The Royal Family are yet to respond to Star's report.