The news comes after a report that Kate’s sister-in-law Meghan Markle is very aware she will become Queen.
"Meghan is very aware that Kate will be Queen; their roles are very clear," the source told PEOPLE.
"Meghan doesn’t fit the mould, while Kate was groomed for this," the source dished, before adding that in comparison the former Suits actress was a "fully formed person" before she married into the Royal Family.
The source goes on to explain that both women find it challenging when they are pitted against each other.
"What’s challenging is when they are pitted against each other. That’s been challenging to both of them.
"Meghan has her life, Kate has hers."