When Meghan Markle walks down the aisle of St. George's Chapel in Windsor Castle on Saturday, May 19, her dress will no doubt be beautiful -- but it will also undoubtedly be in adherence to a number of long-held traditions most people don't even know exist.

Long sleeves

Royal brides are expected to maintain a certain level of modesty when it comes to their wedding gowns. Because of this, it has become tradition, albeit an unofficial one, that royal wedding dresses feature long sleeves.

So, while lesser-known British royals like Lady Helen of Windsor have opted for gowns that show off their arms, those at higher-profile ceremonies usually end up with a more classic, long-sleeved look. For example, Kate Middleton (now the Duchess of Cambridge) wore a Sarah Burton for Alexander McQueen gown with intricate lace sleeves. Harry's mother, Princess Diana, wore a gown by David and Elizabeth Emanuel that also featured dramatic sleeves, though hers were more voluminous, ruffled silk taffeta. And Harry's grandmother, Queen Elizabeth II, married in a long-sleeved satin gown by designer Norman Hartnell back in 1947.

Meghan Markle's gown may harken back to her American roots -- and Hollywood at that -- but it's difficult to imagine her breaking from this tradition on May 19.

It's tradition that her bouquet contain myrtle

Every royal bride since Queen Victoria has carried a sprig of myrtle in her bouquet. Queen Elizabeth did it. Princess Diana did it. Kate did it. And it would be highly unusual if Meghan Markle didn't follow in their footsteps. Myrtle is viewed as an emblem of marriage and love, but its significance for the royals goes far deeper than that.

When Queen Victoria got married to Prince Albert in February 1840, Albert's grandmother gifted the young bride-to-be a sprig of myrtle. Queen Victoria later planted that sprig in the garden outside her home on the Isle of Wight. Then, when her daughter got married in 1858, she carried a sprig from that plant in her bouquet. And ever since, royal brides have opted to do the same -- most even go so far as to include a sprig from Queen Victoria's original garden of myrtle. In fact, that garden opened to the public for the first time in June 2017, so that royal fans could see and smell the famous myrtle firsthand.

A few royal brides, however, have chosen to include myrtle from a different source. When Prince Charles wed Camilla Parker Bowles in 2005, for example, the bride chose instead to include a sprig from a supporter in Cornwall.

Lace

While there are a few exceptions, most high-profile royal brides have either worn lace dresses or dresses of a different material that still incorporate lots of lace. In fact, the most recent example, Kate's 2011 Alexander McQueen gown, was reminiscent of the lace dress worn by American actress Grace Kelly at her 1956 wedding to Prince Rainier III of Monaco. In 2013, Princess Claire of Luxembourg opted for a long-sleeved lace gown as well. In 2015, so did Princess Sofia of Sweden. Now, experts are predicting that Meghan Markle will likely follow in their footsteps.

Royal brides do not show their shoulders or cleavage

While Kate's wedding dress had a low-cut V-neckline for a royal gown, royal brides never bare their shoulders and avoid showing too much cleavage. So, on her wedding day in 1960, Princess Margaret, the queen's sister, wore a Norman Hartnell gown of silk organza which featured one of the slenderest v-necks you've likely ever seen. Likewise, in 1995, Princess Marie-Chantal of Greece chose a lace gown with a turtleneck in adherence to this tradition of modesty.

A tiara to top it all off

Most of the British royal brides in recent memory have adorned their bridal looks with diamond tiaras. Princess Diana famously wore her family's Spencer tiara when she married Prince Charles in 1981. In 2011, the queen loaned Kate the Cartier Halo tiara for her walk down the aisle to marry Prince William. And the Queen Mother, Lady Elizabeth Bowes-Lyon, wore a tiara of wild roses set amidst rose-cut diamonds.

Many royal experts speculate that Meghan Markle will continue the tradition by sporting a diamond tiara, either from the queen's personal collection or from that of Harry's mother.

You may now not kiss the bride

Lastly, unlike most American weddings which culminate in the iconic line, "You may now kiss the bride," royal weddings rarely do.

In fact, the Church of England actually forbids such acts in sacred places like Westminster Abbey. That's why William and Kate shared their first kiss as a married couple on a balcony outside Buckingham Palace. Thus, we are unlikely to see a kiss between Prince Harry and his new bride, Meghan Markle, during the actual ceremony at Windsor Castle. For that memorable moment, royal fans will simply have to wait and see.

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