The highly trained armed protection officer is being brought in after the latest anthrax scare to hit the famous couple.
The tough measures follow the incident when white powder – which turned out to be harmless – was sent to the couple at St James's Palace last month.
Both Harry, 33, and Markle, 36, have been warned of the dangers and their will be unprecedented security at their wedding which takes place on Saturday May 19, 2018, at St. George's Chapel at Windsor Castle.
Royal security chiefs will draft in the crack guard in a footman's uniform to counter fears of an attack at the ceremony.
A source said: "It's an unusual step, but they need somebody right on their shoulder who can act immediately. It's going to be a huge public event, and Meghan and Harry will be afforded the best protection there is."
The event that will be seen by millions around the world presents a security headache for the police in the UK.
Anti-monarchy protestors are threatening chaos by dressing up as homeless people along the procession route on May 19 while 2,640 members of the public invited to Windsor Castle grounds.
The source said: "People in charge of security aren't taking any chances. It's going to be a huge event, they can't be too careful.
"The anthrax scare confirmed the couple are an increasing targets for fanatics."
All guests will be completely vetted while armed undercover cops will mingle with the crowds watching the procession as helicopters monitor things from the air.
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