The Duke and Duchess of Sussex, Prince Harry and Meghan Markle, have faced heavy criticism after reportedly failing to respond to King Charles III's coronation invitation by the Monday deadline. The coronation is set to take place in May.

Rafe Heydel-Mankoo, a royal commentator and expert in monarchy, protocol, honors, and British traditions, condemned the couple as "rude" for not clarifying their attendance at the historic event. He theorized that they are attempting to capitalize on the coronation invitation for publicity purposes, as they become "increasingly irrelevant."

During an interview with GB News, the royal expert stated, "It's actually, I think, a shameful publicity ploy by the Sussexes, and they're milking this for all it is worth." He added, "They know that essentially, with their distance from the royal family, they're becoming increasingly uninteresting to the public at large, increasingly irrelevant. This is a way to keep them in the headlines and on the front pages."

Heydel-Mankoo went on to say, "It actually makes them seem to be powerful with the royal family seemingly trying to entice them over the pond. But this is really quite narcissistic because, at the end of the day, this is about celebrating the King. All attention must be on the monarchy and on the King."

The author of "A London Peculiar: The London You Shouldn't Miss" accused the Sussexes of being "childish, self-centered, and self-obsessed" for not responding promptly to the invitation to King Charles' coronation.

Heydel-Mankoo claimed, "It's absolutely rude. This whole entire 'will they or won't they' drama is actually getting really tedious now. That is precisely what the King and the royal family don't need."

Despite the controversy surrounding the couple, Heydel-Mankoo noted that it would be worse for King Charles if they do not attend the coronation in London on May 6.

Some observers speculate that the royal couple may still attend the event, even after missing the RSVP deadline.

Journalist and royal author Christopher Andersen told Fox News Digital, "it's not too late for Harry to put on his big boy pants and go."

Andersen believes that if Prince Harry attends, he would want Meghan to accompany him. He stated, "Going solo might imply that Harry has chosen his family over his wife, and above all else, the Sussexes want to make it clear they are an unbreakable team."

However, Andersen suggested that if the Duke and Duchess of Sussex do decide to attend, they should prepare for a "frosty" reception from the royals during the coronation, and they will need to "stiff-upper-lip it."