With less than six weeks to go before Meghan Markle and Prince Harry's wedding day, royal watchers have turned to speculation on which tiara Markle may borrow for her wedding at St. George's Chapel.

Royal brides have typically worn a headpiece from the extensive royal vault of jewels.

PHOTO: Britain's Prince Harry and his fiancee actress Meghan Markle arrive to meet participants at the UK team trials for the Invictus Games Sydney 2018 at the University of Bath Sports Training Village in Bath, England, April 6, 2018.
Ben Stansall/AFP/Getty Images
Britain's Prince Harry and his fiancee actress Meghan Markle arrive to meet participants at the UK team trials for the Invictus Games Sydney 2018 at the University of Bath Sports Training Village in Bath, England, April 6, 2018.

Here are some of the popular tiaras donned by royals in the past:

Spencer tiara

Princess Diana wore the family heirloom for her wedding to Prince Charles in 1981, as did her two sisters. The stunning tiara is now in the possession of Diana’s brother, Lord Charles Spencer.

PHOTO: The Prince and Princess of Wales return to Buckingham Palace by carriage after their wedding, July 29, 1981.
Princess Diana Archive/Getty Images
The Prince and Princess of Wales return to Buckingham Palace by carriage after their wedding, July 29, 1981.

While many royal watchers deem it unlikely, Harry may ask if his bride can borrow the tiara for sentimental reasons.

PHOTO: Diana, Princess of Wales, wearing the Spencer family tiara and crescent shaped diamond and sapphire earring, necklace and bracelet given to her by the Sultan of Oman attends a banquet, Nov. 2, 1987 in Bonn, Germany.
Anwar Hussein/Getty Images, FILE
Diana, Princess of Wales, wearing the Spencer family tiara and crescent shaped diamond and sapphire earring, necklace and bracelet given to her by the Sultan of Oman attends a banquet, Nov. 2, 1987 in Bonn, Germany.

Harry, 33, and Markle, 36, have included a nod to Harry's late mother as they plan the wedding, with Markle's ring including two diamond stones from Diana’s jewelry collection.

PHOTO: Britain's Prince Harry holds hands with Meghan Marklem wearing an engagement ring in the Sunken Garden of Kensington Palace, London, Nov. 27, 2017.
Toby Melville/Reuters
Britain's Prince Harry holds hands with Meghan Marklem wearing an engagement ring in the Sunken Garden of Kensington Palace, London, Nov. 27, 2017.

Lotus Flower tiara

Princess Kate wore the Lotus Flower tiara at a state dinner at Buckingham Place honoring Chinese President Xi Jinping in 2015.

PHOTO: Chinese President Xi Jinping and Catherine, Duchess of Cambridge attend a state banquet at Buckingham Palace, Oct. 20, 2015, in London.
Dominic Lipinski/Pool/Getty Images
Chinese President Xi Jinping and Catherine, Duchess of Cambridge attend a state banquet at Buckingham Palace, Oct. 20, 2015, in London.

The tiara was a favorite of Queen Elizabeth’s sister, Princess Margaret, and is not as heavy as some of the other tiaras in the royal collection.

It is a distinct possibility Markle could wear this tiara, passed down through the Windsor women.

Princess Diana’s emerald choker

The emerald and diamond choker, which Harry's late mother also wore as a headband, is one of the most iconic pieces associated with the late Princess of Wales. Designed by Garrard in the 1920’s for Queen Mary, the necklace was a wedding gift to Diana from Queen Elizabeth.

PHOTO: Prince Charles dancing with his wife, Princess Diana, during their official tour of Australia, Oct. 1, 1985, in Melbourne, Australia.
Tim Graham/Getty Images
Prince Charles dancing with his wife, Princess Diana, during their official tour of Australia, Oct. 1, 1985, in Melbourne, Australia. The Princess is wearing a diamond and emerald choker (a wedding gift from the Queen) as a headband with a one-shouldered turquoise satin organza dress designed by David And Elizabeth Emanuel.

Kate has never worn the piece and royal brides have been known to refashion pieces from the extensive jewelry collection that exists.

Markle and Harry could adapt the necklace associated so closely with Diana to create an unforgettable, one-of-a-kind sentimental piece that Markle could wear even after her wedding day.

Diana also had a sapphire and diamond choker that could be similarly created into a tiara for Markle's wedding day.

Cambridge Lovers Knot tiara

Diana’s favorite tiara was created by the Queen Elizabeth’s grandmother, Queen Mary, in 1913. It was a gift to Diana on her wedding from the monarch.

PHOTO: Princess Diana, Princess of Wales wearing a tiara in New Zealand during April 1983.
Anwar Hussein/WireImage/Getty Images
Princess Diana, Princess of Wales wearing The Cambridge Lover's Knot Tiara in New Zealand during April 1983.

When Diana died in 1997, it was returned to Queen Elizabeth.

Diana said the tiara was made of 19 diamond arches and stunning hanging pearl drops. Kate has now borrowed and worn the tiara several times as the Duchess of Cambridge, reflecting the tiara’s historical provenance and name.

PHOTO: Catherine, Duchess of Cambridge departs after attending the annual Diplomatic Reception at Buckingham Palace, Dec. 8, 2016, in London.
Max Mumby/Indigo/Getty Images
Catherine, Duchess of Cambridge departs after attending the annual Diplomatic Reception at Buckingham Palace, Dec. 8, 2016, in London.

It may not be the first choice as a wedding tiara for Markle since Kate has started wearing it to various state functions.

Cartier Halo Scroll tiara

Kate donned the Cartier halo tiara for her wedding to Prince William in 2011, so it’s probably unlikely Markle would borrow the same tiara from Queen Elizabeth for her wedding to Harry.

PHOTO: Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge on the balcony at Buckingham Palace, following their wedding at Westminster Abbey, April 29, 2011, in London.
Mark Cuthbert/UK Press via Getty Images, FILE
Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge on the balcony at Buckingham Palace, following their wedding at Westminster Abbey, April 29, 2011, in London.

The tiara, which once belonged to the Queen Mother, would be an elegant yet understated piece for Markle.

Diana’s jewels

While many brides dream of being a princess for a day, Markle's humble beginnings will see the California native celebrating her own fairy-tale ending.

She will have access to some of the spectacular jewels in Diana’s personal jewelry collection, which were not returned back to Queen Elizabeth and left to her two sons, William and Harry.

After Diana's death, in a "Letter of Wishes" which became part of her will, Diana explained that she was passing her priceless jewelry to her sons so their future wives would one day have to use.

PHOTO: Princess Diana and her sons Prince Harry, and Prince William, as they gather for the commemorations of VJ Day in London, Aug. 19, 1995.
Johnny Eggitt/AFP/Getty Images, FILE
Princess Diana and her sons Prince Harry, and Prince William, as they gather for the commemorations of VJ Day in London, Aug. 19, 1995.

"I would like you to allocate all my jewelry to the share to be held by my sons, so that their wives may, in due course, have it or use it," the letter reads. "I leave the exact division of the jewelry to your discretion."

One of the most jaw-dropping pieces in Princess Diana’s jewelry box was the sapphire and seven-strand pearl choker she wore before and after her divorce from Prince Charles.

PHOTO: Diana, Princess of Wales, wearing  a sapphire diamond and pearl necklace, attends a banquet on April 16, 1986 in Vienna.
Anwar Hussein/Getty Images, FILE
Diana, Princess of Wales, wearing a sapphire diamond and pearl necklace, attends a banquet on April 16, 1986 in Vienna.

Princess Kate has never worn the iconic necklace. She has regularly worn other pieces in Diana’s extensive collection so it may have been one item William and Harry decided to save for Harry's future wife.

The sapphire was initially given to Diana, the Princess of Wales, by the Queen Mother as a wedding gift and she later refashioned it into the necklace.

Diana was also gifted an extensive collection of sapphires by the Saudi Crown prince on her wedding day, which she wore throughout her life.

William presented Kate with a pair of sapphire earrings matching Diana’s engagement ring, believed to be from Saudi sapphires.

PHOTO: Catherine, Duchess of Cambridge leaves St Paul's Cathedral after a Service of Commemoration for troops who were stationed in Afghanistan, March 13, 2015 in London.
Chris Jackson/Getty Images
Catherine, Duchess of Cambridge leaves St Paul's Cathedral after a Service of Commemoration for troops who were stationed in Afghanistan, March 13, 2015 in London.

There are several pieces that Kate has never worn from the collection that we may see Markle make her own in the years ahead.