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Meghan Markle will reportedly attend Pippa Middleton's upcoming wedding to financier James Matthews as Prince Harry's date. But the actress won't attend the ceremony at St Mark's church in Engelfield, England on May 20 as protocol prohibits unmarried and unengaged partners to attend the event.

A source reveals to PEOPLE that Meghan will be by Prince Harry's side when attending the evening party after the nuptials. The source explains while the "Suits" actress is not allowed to attend the ceremony, she and her prince beau are more likely to attend the party afterwards, which tends to be less formal.

Founder and director of Beaumont Etiquette Myka Meier says it's not surprising that Meghan didn't get invite even though there's no formal "no ring, no bring" rule. "I would not be surprised if Prince Harry was not given a plus one, as the wedding guest list would have most likely been made in fall of last year when Prince Harry's relationship with Meghan was not as public," Meier says.

She continues, "I typically recommend if someone is married, engaged, considers themselves to have a serious significant other, or is traveling in for the wedding, they should receive a plus one." Meier adds, "Pending how intimate Pippa wants to keep her wedding, she may very well follow the 'no ring, no bring' rule."

This won't be the first time that Meghan has accompanied Prince Harry to a wedding. The 35-year-old actress and the 32-year-old royal redhead, who have been dating for nearly a year, attended his best friend Tom "Skippy" Inskip's wedding in Jamaica. The prince brought his actress girlfriend since it was "a big event" for him as he became the best man.