"Sam will be a huge loss," a source close to Meghan told the newspaper.
"Going forward, Meghan might need someone cut from a slightly different cloth to traditional courtiers, who is not a career civil servant or royal insider."
This is yet another big resignation for the house of Sussex.
Meghan's personal assistant Melissa Touabti who was instrumental in the royal wedding preparations, quit after six months into her job.
It was reported that Touabti found the Duchess to be "difficult".
And she's not alone, according to several insiders saying that Kate Middleton has had run-ins with her sister-in-law.