Kate Middleton wore Queen's necklace and low cut dress to outshine Queen Letizia

Kate Middleton has a fashion rival in town as Queen Letizia has often been dubbed Spain's version of the Duchess of Cambridge.

Despite often playing it safe when it comes to style, Kate, 35, ensured she was not outshone by the Spanish queen and former news anchor Letizia, 42, in a sensational low-cut pink gown by Marchesa.

The dusty pink number is probably her most sexy ensemble to date with its plunging neckline and sheer lace bell sleeves for an extra feminine touch.

And the duchess didn't stop there. She accessorised the high fashion gown by dipping into the Queen's jewellery box and reaching for a piece that hasn't been seen for decades.

Taking her outfit to the next level for Wednesday night's (12 July) state banquet in honour of King Felipe and Queen Letizia at Buckingham Palace with the Queen, Prince Philip and her husband Prince William, Kate called upon the services of the Cambridge Lover's Knot Tiara.

She has worn it for the past two Christmas diplomatic receptions at Buckingham Palace and complimented it with her favourite diamond and pearl earrings.

The tiara was made by Royal jewellers Garrard in 1914 to a personal design by Queen Mary – and was a copy one owned by her grandmother.

Princess Diana later received it as a wedding present from the Queen, but it is reportedly so heavy that it gave her headaches when she wore it.

But it was Queen Elizabeth II's statement Bandeau Necklace that almost stole the show entirely with its opulent diamond and ruby design bought from the jeweller Boucheron in 1907 by society figure Lady Greville. She left it to her friend the Queen Mother upon her passing in 1942.

The Queen Mother later gave the stunning piece of jewellery to the then Princess Elizabeth as a wedding present from her parents. Now that's a necklace with some history.

Royal watchers were quick to comment on the duchess' effort for the special dinner, with one person tweeting: "I just can't get over this neckline on Kate, it's just sooo beautiful on her"

Someone else commented: "Kate looks hot, no doubt! Like the front of this dress is full on SLAY and I'm LIVING. #sorrynotsorry"

Meanwhile, Queen Letizia put on an extremely stylish display in an off-shoulder red embroidered gown by her go-to designer from Spain, Felipe Varela.

The royal lived up to expectations in the embellished dress which she teamed with Cartier earrings and a clutch by Magrit. Like the duchess, she wore a tiara, and hers is known as La Buena.