Kate Middleton sparks major debate over 'new appearance change' as fans left confused by one detail

Kate Middleton has left fans scratching their heads after her latest outing - and it's all to do with her hair.

The Princess of Wales, 43, officially debuted her new blonde locks last week, swapping out her usual chestnut brown tresses for a much lighter look.

Making a surprise appearance on September 8 to visit the new gardens at London's Natural History Museum, Kate and hubby Prince William returned to their royal duties after their summer break.

She wore her long hair in loose curls and looked fashionable as ever in a brown blazer layered over a white shirt for the official outing.

Kate first gave fans a glimpse of her new hairstyle last month, when she and William were seen through the car window on their way to a church service in Scotland with their three children: Prince George, 12, Princess Charlotte, 10, and seven-year-old Prince Louis.

And fans have been complimenting the princess on the big change, writing on social media: "That's a gorgeous colour!" and "Talk about a hair transformation."

Some of the new snaps appear to show Kate's hair looking slightly darker (WPA Pool/Getty Images)

But now, fans have been left confused as a few pictures from Kate's latest outing on Monday (September 8) showed her hair looking somewhat brunette again.

She and William visited the National Federation of Women's Institute (WI) to commemorate the three-year anniversary of the death of Queen Elizabeth II.

He and Kate joined WI members for a slice of cake, chatting fondly about his late grandmother’s passion for horses, in tribute to his grandmother's decades-long association with the organisation.

And snaps from the visit appear to show Kate's locks looking darker again, which royal family fans have quickly picked up on, questioning whether she's actually changed it again or if it's simply a trick of lighting and angles

The New York Post reported that the princess has 'returned to her classic brunette look' after getting backlash from cruel trolls about her blonde hair.

However, Twitter users were quick to point out that it likely is the same hair, it just looks different scraped back in another hairstyle.

"It's the same hair colour, just in different lighting. Catherine doesn't listen to trolls - she colours her hair whatever colour she bloody wants," one user wrote.

While a second agreed: "It’s the exact same hair - she just pulled it back, and the outdoor lighting made it look a bit more blonde."

The Princess of Wales debuted her new blonde look last week (Chris Jackson/Getty Images)

And a third and fourth wrote: "lol.. it is the same colour" and "Same colour. Different lighting. A different angle shows her highlights."

Others have simply expressed frustration over the speculation and affirmed that it of course, doesn't really matter what colour her hair is.

They wrote: "Poor Kate! Doesn't get to experiment with a new look. She is a natural beauty - she can shave her head and still be beautiful. All the best to her."

Someone else added: "She did not 'return'. It's the same hair with the same highlights in the top layer. Pulling her hair back just exposed her natural hair colour beneath."

And this does make sense, as when you look at the other photos from the event, some show that her hair is still lightened.

Either way, we love the new look!