"Melissa is a hugely talented person", the source said.
Meghan eventually opted for the Queen Mary Diamond Bandeau, which dates from 1932.
Meghan had reportedly picked a tiara with emeralds but she was told she couldn't wear it given its history couldn't be established and that it might have originated Russian Federation.
"There was a very heated exchange that prompted the Queen to speak to Harry".
Their source claims Meghan wanted a tiara that featured emeralds, but the loved-up couple were told it would be impossible due to lack of info on the tiara's origin, with fears it could be of Russian heritage.
A Kensington Palace spokesman declines to comment on the departure of the PA, whose name is given only as Melissa. "There were concerns it could have come from Russian Federation originally".
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"She said, "Meghan can not have whatever she wants".
To which William added: "I know, I've got serious OCD on light switches now, which is awful".
Melissa reportedly worked hard on planning the 19 May wedding at Windsor Castle with Meghan and Prince Harry and would have helped smooth things over as the Markle side of Meghan's family began acting up in the days leading up to the ceremony.
According to Jobson's new book, the Queen warned Harry that Markle needed to mind how she spoke to staff and to make sure she follows "family protocol".
"However, there's a different degree of respect in the royal household and Kate has always been very careful about how she has acted around staff".
"Meghan can be hard".
Meghan's former agent, Gina Nelthorpe-Cowne, described her before the wedding as unique in her determination to succeed.