She's not put a foot wrong in the style stakes since commencing royal duties, but Meghan Markle made a rare fashion faux pas as she visited Birmingham with Prince Harry last week.

The bride to be looked chic in a $298 navy Italian stadium-cloth wool coat by J. Crew for the visit but overlooked a crucial detail when getting dressed.

Meghan failed to remove the loose criss-cross stitching that holds together the vent on the back of the coat, with the white thread showing up against the navy wool of her coat.

The 'X' stitching, also known as a tailor's tack, is designed to keep the shape of the garment while it is being transported or on display.

Meghan looked chic in her J. Crew coat, but she forgot to remove the tailor's tack at the back. Photos / Getty Images
Meghan looked chic in her J. Crew coat, but she forgot to remove the tailor's tack at the back. Photos / Getty Images

But the stitching should be removed once the garment has been bought - and certainly before it is worn for the first time.

The same rule applies for the vents on other tailored pieces, such as pencil skirts and suit jackets.

Previously, fashion guru Hannah Almassi, of Who What Wear revealed that failing to remove the stitching changes the shape and fit of the coat.

She explained: "If you don't, the tailored silhouette doesn't sit right.

"The hem will instead heave and stretch to fit around the body, rather than just skimming in the most flattering way."

While she may have made a small fashion misstep on her visit to Birmingham, Meghan is naturally pulling out all the stops to ensure she wows on her upcoming wedding day.

Last months, rumours swirled that she had chosen Alexander McQueen as her wedding dress designer, following in the footsteps of the Duchess of Cambridge.

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Bookies suspended betting on the designer after receiving a flurry of punts on McQueen.

However, the rumours may have been off the mark as a royal source has claimed Meghan has chosen Ralph & Russo, the designers behind her opulent engagement shoot dress.

Priced at a staggering $106,704, the outfit comprised a silk organza skirt, hand appliqued with silk tulle ruffles, and a sheer bodice decorated with intricate gold feather thread-work and beads.

If the well-placed informant is correct, the decision by Prince Harry's bride to select a British brand would provide a welcome boost for this country's fashion industry

Based in a seven-storey Mayfair salon overlooking the gardens of Buckingham Palace, Ralph & Russo was the first British fashion house to be invited to the Paris couture shows in a century.

With prices starting at $57,183 and customers admitted by appointment only, it could provide the expected combination of royal elegance and Hollywood glamour.

It specialises in elaborate couture dresses studded with crystals, feathers, iridescent metallic features and floor-sweeping trains.

Adored by A-list Americans such as Beyonce and Gwyneth Paltrow, Ralph & Russo made the skirt suit that Angelina Jolie wore to accept her honorary damehood from the Queen in 2014.