The source added to "Entertainment Tonight": "Like Kate, expect Meghan to make the occasional nod to her husband's fashion icon mother".
"It was first used in connection to Meghan in the November engagement announcement and since then has been used throughout the royal household's communications, on press releases, invitations, and social media", he went on.
"Members of the Household Cavalry will form a staircase party at St George's Chapel, Windsor Castle as part of the wedding". After the ceremony, the couple is expected to have a royal procession from the chapel to the Castle Hill out of Windsor.
About 200 guests have also been invited to an evening reception at Frogmore House, hosted by Prince Charles.
The invitation specified that men wear military uniform or a morning coat and lounge hat, while women are asked to wear a day dress and hat.
In related news, some royal fans reacted to the invitation not using Markle's complete name "Rachel Megan Markle".
The former "Suits" actress is also reportedly set to follow in the footsteps of Catherine - who has four-year-old son Prince George and two-year-old daughter Princess Charlotte, as well as expecting her third child with husband Prince William - when it comes to echoing the fashion sense of Harry and William's late mother Princess Diana, who died in a vehicle crash in 1997.
Richard Fitzwilliams, an expert on the royal family, told The Independentthat as well as being correct etiquette the inclusion of the "Ms" title may show an increasingly progressive stance from the Royal family.