Meghan Markle has already described her dream wedding dress

Markle will wed Prince Harry in May 2018.

— -- When Meghan Markle walks down the aisle in May to wed Prince Harry, all eyes will be on her wedding gown.

Markle, a 36-year-old American actress, became a global fashion trend setter quickly after her relationship with Harry was made public.

A California native, she will have to blend her personal style, which she has described as "California girl" and "relaxed," with the formality of the royal family.

Here is what to know about Markle's style and the tradition of royal wedding gowns as the countdown begins to Markle and Harry's wedding.

Kate's and Diana's royal gowns

The same wedding designer guessing game took place for Princess Kate's 2011 nuptials, and she did not disappoint.

Kate chose a stunning long-sleeved lace and ivory satin dress designed by Sarah Burton, the creative director at Alexander McQueen. The dress was both traditional and modern, with a detailed back, a long train and buttons.

When Harry's mother, Princess Diana, married his father, Prince Charles, in 1981, she wore a dress by husband-and-wife design team David and Elizabeth Emanuel.

The dress, which remained a closely guarded secret until the wedding day, featured a 25-foot train.

Who could design the dress?

At the top of the list to design Markle's wedding dress is Misha Nonoo, a London-raised designer who reportedly introduced Harry and Markle and who has vacationed with Markle.

Nonoo, who designed the "husband" shirt Markle wore to the 2017 Invictus Games, was a finalist for the 2013 CFDA/Vogue Fashion Fund.

Nonoo has a showroom in New York that, combined with her British roots, would help satisfy critics on both sides of the Atlantic.

Jessica Mulroney, Markle's longtime Toronto-based stylist and a bridal expert, is not a designer but will no doubt be at Markle's side advising her on the dress.

Markle will also likely consider two of Diana's longtime favorite designers, Catherine Walker and Amanda Wakeley. Both have couture shops in London's Chelsea district, not far from Kensington Palace, where Harry lives.

Wakeley's designs have been worn by the likes of Kate, Jennifer Lopez, Kate Winslet and Angelina Jolie, but she is best known for her collaboration with Diana in the 1990s.

Walker is the designer most closely associated with Diana's iconic style.

Markle and Harry have said how it important it is that his late mother be represented in their wedding. Markle's engagement ring features two diamonds from Diana's personal collection.

"It is days like — days like today when I really miss having her around and miss being able to share the happy news," Harry said during a joint interview shortly after the two announced their engagement. "But you know, with the ring and with everything else that's going on, I'm sure she's, she's with us."

It would be a sentimental choice and a wonderful surprise for Harry if Markle chooses one of Diana's favorite designers.

"Obviously, not being able to meet his mom, it's so important to me to — to know that she's a part of this with us," Markle said at Nottingham Cottage last week in the interview.

Another possibility to design Markle's gown is Jenny Packham, one of Kate's favorite designers. Packham, who has designed formalwear and gowns for Kate, has a good understanding of what type of dress is required to meet the standards of a royal bride.

Fashion expert Joe Zee, who is a friend of Markle's and interviewed her during New York City Fashion Week in 2015, said he expects she will wear a British designer.

"She's worn a lot of Erdem in the past, so it could be someone like him, but I'm putting my bets on Stella McCartney," Zee said Tuesday on "Good Morning America." "It most likely will not be McQueen, because I feel like Kate owns that."

Markle wore a gown by Erdem Moralioglu, whose line was founded in London, when she accompanied Harry to a wedding in Jamaica in March.

Moralioglu, who was born in Canada to a British mother, has a wide following in the U.S., the U.K. and Canada, making him a great choice as Markle's wedding dress designer.

Markle name-checked several designers when she spoke to Glamour last year about her dream wedding dress.

"Delphine Manivet and Christos Costarellos are faves of mine for their uniqueness and beauty," she said. "And I will always be a fan of Elie Saab. J. Mendel is spectacular as well, especially for more structural designs."

Markle told Glamour the Narciso Rodriguez–designed white dress that Carolyn Bessette wore to her 1996 wedding to John F. Kennedy Jr. is her favorite celebrity wedding dress, calling it "everything goals."

Markle's 'perfect wedding dress'

She has been seen in a princesslike wedding dress before, when her "Suits" character, Rachel Zane, prepared to walk down the aisle last year.

The dress Markle wore for the show was an Anne Barge gown from Kleinfeld in Canada, Glamour reported.

Markle told the magazine that she helped pick the dress for her character, calling it "classic and fairy tale," but said that would not be the dress she would choose for herself.

"It's not my personal style, because I'm a lot more relaxed than Rachel, but I love that I got to play dress-up in this gown," she said, adding that her personal style is "very pared down and relaxed."

"Classic and simple is the name of the game, perhaps with a modern twist," Markle said when asked what she thinks is the "perfect wedding dress." "I personally prefer wedding dresses that are whimsical or subtly romantic."

'A moment of fun and joy'

Harry and Markle will be married at St. George's Chapel at Windsor Castle — a smaller venue than Westminster Abbey, where William and Kate tied the knot, and St. Paul's Cathedral, where Charles and Diana wed.

The choice of the chapel as the venue reflects Harry's and Markle's personal connection to the chapel. While Buckingham Palace is Queen Elizabeth's official residence, she and Prince Philip have always called Windsor Castle home.

Windsor Castle is also close to where Harry spent his early years at Eton, and he and Markle have spent time at Windsor getting to know each other away from the cameras.

"It's a bit smaller. It's outside of London," ABC News royal contributor Victoria Murphy said. "That would just give them the opportunity to maybe have it a little bit more personal, a little bit more low key, which is what Harry can obviously do, since he's not going to be the king."

Like any bride, Markle will choose a dress that reflects her style and sensibilities. Holding the wedding ceremony at St. George's Chapel could allow her to choose a dress that more closely fits her relaxed style.

Harry's communication's secretary Jason Knauf said Tuesday the two want their wedding day to be fun and reflective of their relationship.

"This wedding, like all weddings, will be a moment of fun and joy that will reflect the characters of the bride and groom," he said.