Striking ... The Duchess of Cambridge wore a birght red dress and clutched a small red bag and Strathearn tartan scarf.

Striking ... The Duchess of Cambridge wore a birght red dress and clutched a small red bag and Strathearn tartan scarf. Photo: AFP

The Duchess of Cambridge wowed the crowd in another Alexander McQueen number as she arrived for the diamond jubilee river pageant with Prince William and Prince Harry.

All eyes were on Kate as she stopped to talk to onlookers at Chelsea pier, wearing a striking bright red dress by the same designer who created her much-admired wedding gown.

Clutching a small red bag and Strathearn tartan scarf - a nod to her Scottish title, the Countess of Strathearn - she paused to accept a bunch of white roses and heather from five-year-old Henry Moffat.

Dressed to impress ... from left to right, the Queen, the Duchess of Cornwall and the Duchess of Cambridge.

Dressed to impress ... from left to right, the Queen, the Duchess of Cornwall and the Duchess of Cambridge. Photo: AFP

Kate's maritime-themed brooch featured two silver dolphins and was a gift from the Royal Navy Submarine Service, of which William is Commodore in Chief.

The Duchess, who teamed her dress with nude heels, wore delicate drop earrings and a Sylvia Fletcher hat.

Her hair was safely held in place away from the wind in a half up, half down do.

The Duchess of Cambridge ... she teamed her dress with nude heels.

The Duchess of Cambridge ... she teamed her dress with nude heels. Photo: Getty Images

One fashion expert said the outfit was a vibrant but safe choice, which allowed the Queen to shine on her big day.

Carly Wood, who set up the katemiddletonstyle.org blog, said: "I was assuming she'd go for red, white or blue today. I love that it's bright and vibrant and a nice contrast to the weather.

"It's a little safe in my opinion, but then I expected that - it is after all the Queen's big day and the Queen should take centre stage - not Kate and her outfit."

Royla couple ... Prince William, and his wife, the Duchess of Cambridge, arrive to board the royal barge.

Royal couple ... Prince William, and his wife, the Duchess of Cambridge, arrive to board the royal barge. Photo: AFP

The dress is 2011 Alexander McQueen and was also worn, without sleeves, by reality TV star Kim Kardashian and Tulisa Contostavlos at the X factor auditions last year.

Kate's version had full-length sleeves.

Harold Tillman, chairman of the British Fashion Council, described Kate's ensemble as "chic perfection" and the Queen's outfit as having a "timeless elegance".

Smile for the cameras ... all eyes were on the Duchess of Cambridge

Smile for the cameras ... all eyes were on the Duchess of Cambridge Photo: AFP

The monarch's Angela Kelly silver and white dress and coat was created from white boucle, a fabric that has a fine textured feel, and threaded throughout with silk ribbon.

The material was embroidered with gold, silver and ivory spots and embellished with Swarovski crystals to reflect the River Thames.

"Timeless elegance is what she always portrays," Tillman said.

"It was outstanding - beautiful fabric.

"It got my vote. It's a difficult job being up to date and staying regal.

"She picks the right look for the right occasion for the right country."

Tillman also praised the Duchess of Cornwall's Anna Valentine outfit, saying: "A great colour. It suited her."

Camilla wore an Anna Valentine coat and dress and Philip Treacy hat.

Princess Eugenie wore a coral Roland Mouret dress with a Moschino cardigan, LK Bennett shoes and black and coral Stephen Jones hat.

Princess Beatrice's silver and pink hat was by Stephen Jones. She also wore a Suzannah silver and navy dress and navy blue coat by Marni.

PA