The royal wedding will take place on May 19 at St. George's Chapel in Windsor, England, in front of all the British monarchy, family, friends, spectators and millions of people watching around the world. While all eyes will be on Meghan and her gown, there will also be a slew of celebrity guests in attendance.
So what does one wear to the wedding of the year? ET is rounding up eight rules that guests must follow when dressing for the special day.
1. Gentlemen must wear a "uniform, morning coat or lounge."
For non-royalty, men can don "morning dress" attire, which means that most will be suited in a morning coat, waist coat, tie and striped trousers. David Beckham perfectly showcased the outfit below. Additionally, male attendees can also opt for a "lounge suit," which is a basic suit.
2. Ladies should accessorize "with a hat."
In England, one of the most important accessories is a hat or fascinator.
"For a royal wedding, especially in England, it has to be the hat," Louise Green, a British milliner who has been making hats for 30 years in the US, told ET. "Whether you start with the hat and then buy the outfit, or buy the outfit and then buy the hat, you have to have a hat. You can't go to the royal wedding without a hat."
What many people will be spotted wearing are fascinators. "A fascinator is a small hat, usually it's a headpiece," Green explained. "It will be affixed to the head, either with a headband or a comb or elastic, and it covers part of the head whereas a hat covers the full head."
Though, there are certain rules when it comes to wearing a hat in the church. For example, "It wouldn't be polite to be wearing a huge hat in the church because then you'd be blocking someone's view behind you," Green said. The base of the fascinator has to be four or five inches, but you can't just wear a headband.
3. Women must cover their shoulders.
There are a lot more rules for women to follow when it comes to dressing for a royal wedding. All ensembles must be on the conservative side and cover their shoulders when entering the church. Victoria Beckham had the right idea at William and Kate Middleton's celebration.
"You're going to see classic clothing," Green explained. "They've already said you have to cover your shoulders... There's not going to be anything provocative in dressing."
"But then they can go wild with the hat," she added.
4. Dresses have to be down to the knee.
The same goes for the length of the dress and its hemline. No showing off too much leg and keep the dress at a respectable knee-length.
5. White and cream colors are reserved for the bride and wedding party.
Kate was her sister, Pippa Middleton's, maid of honor on her wedding last May, so naturally the Duchess of Cambridge was permitted to wear a blush-toned dress. Though, in many cultures it's inappropriate for guests to wear the same color as the bride.
6. Women can't wear wedges.
This rule may be a bit biased, as Queen Elizabeth is said to not be a fan of the chunky footwear.
“The queen isn’t a fan of wedged shoes,” a source previously told Vanity Fair. “She really doesn’t like them and it’s well known among the women in the family.” Kate used to be spotted wearing the shoes all the time, but never around Her Majesty. So, assume they're a no-go for Harry and Meghan's nuptials.
7. Members of the royal family must wear neutral-colored nail polish.
According to the royal dress code, women in the royal family can only use nude-colored shades. Meghan and Kate are frequently spotted with nude or soft cream-colored manicures -- and the royal wedding should be no exception for them.
8. Women should wear tights.
Another one of Queen Elizabeth's rules is that a royal must never be without their nude stockings. Kate, the late Princess Diana and the queen herself have all worn pantyhose while on royal events. Meghan has broken this guideline a handful of times, but she did abide by the rule when she attended the Commonwealth Service with Harry's grandmother.
Though, it's up to the wedding guests if they will follow this unofficial rule -- but if the queen is there, it's probably a good option.