While some have voiced confusion at the rule, with Kate also born a commoner, it apparently all stems from when the rules were updated in 2012, after she married Prince William.
At the actual royal wedding, Markle's friend Serena Williams and the Beckhams are expected to be in attendance.
Victoria famously shunned public appearances after the death of her husband, Prince Albert - a tragedy that had occurred only 15 months prior to Bertie's wedding to Alexandra. The one hour show will have Six Opinionated Wedding-istas including David Emanuel, Randy Fanoli, Jo Cooke, Alison Law, Olivia Buckland and Alex Bowen gawping at the spectacle, gasping at the glamour, gushing at the fashion highs and gagging at the fashion lows. They will also line the streets from the castle to St. George's Chapel, the venue of the wedding.
People from all across the globe have their eyes set on Prince Harry and Meghan Markle's grand wedding. Crowds will get to see Harry in his military uniform as the pair arrive on foot and make their way to the Chapel's West steps.
CBS News will have full coverage of the royal wedding on May 19, starting at 4 a.m. ET, anchored by Gayle King and "Entertainment Tonight's" Kevin Frazier.
7pm: The bride and groom will depart Windsor Castle around this time for their evening reception at Frogmore House, hosted by Prince Charles. But the world will have to tune in to see Markle's wedding dress and other surprises. "This one is a little bit more special having known the man - and everyone loves a wedding".
The 20-minute broadcast features a revealing interview given by Prince Harry and Meghan Markle in November previous year when the couple announced their engagement. You can buy tickets and search for a movie theater near you here.