By GINA KALSI, FEMAIL REPORTER and JANE HERZ, US FEMAIL REPORTER

Royal fans who were hoping to spot Melania Trump perfoming a traditional curtsy when she met the King and Queen today were left disappointed, after the First Lady greeted her hosts with a handshake on arrival at Windsor Castle.

Neither the First Lady, 55, nor President Donald Trump, 79, bowed before Charles, Queen Camilla, or Kate and William at the start of their historic state visit.

While members of the public, politicians and even more junior members of the royal family observe tradition when greeting the King and Queen and the Princess of Wales, there is no requirement for visiting head of state to do so.

According to the Royal Family website, there is no obligation for members of the public to curtsy or bow to members of the Royal Family, but many do wish to observe tradition.

For men this is a neck bow and women a small curtsy, but shaking hands is perfectly acceptable.

Within the Royal Family, everyone is expected to bow or curtsy to the King and Queen, or anyone of a more senior rank.

However, Kate only outranks blood members of the Royal Family when she is with her husband. If she is alone with those who are royal through blood, such as Princess Anne and Princess Beatrice, they rank above her.

Eagle-eyed royal fans may have noticed that Melania Trump, 55, did not bow for King Charles or Queen Camilla during their state visit on Wednesday (pictured)

King Charles receives US President Donald Trump and First Lady Melania Trump at Windsor Castle in Windsor on Wednesday

During their first State Visit in 2019, Trump briefly nodded his head to the late Queen Elizabeth, although royal watchers again pointed out that Melania did not curtsy.

And they are not the only ones who have opted for handshakes in the past. During Barack and Michelle Obama's State Visit in 2011, neither he nor his wife bowed to the late Queen.

In 2009, Michelle reportedly curtsied when she first met Queen Elizabeth in her private apartments, but made headline news during the Buckingham Palace reception when she decided to embrace her.

Other international Royal Families are also exempt from the rule, as seen in 2017 when King Felipe and Queen Letizia of Spain also met Queen Elizabeth and the Duke of Edinburgh during a State Visit.

Letizia went to shake the late Queen's hand, while Felipe opted to kiss her on the cheek and then her hand when they arrived.

During her second State Visit on Wednesday, Melania Trump looked effortlessly chic in a Christian Dior Haute Couture dark gray skirt suit that flared out at the waist and fell just below her knees.

She wore her blonde tresses in a slick bun that was largely hidden by a wide-brimmed wool hat in a brighter purple hue.

Melania was expertly poised in her heels as she walked alongside Donald, Prince William and the Princess of Wales in the Walled Garden on the Windsor estate.

During her second State Visit on Wednesday, Melania Trump looked effortlessly chic in a Christian Dior Haute Couture dark gray skirt suit

The group walked a short distance to meet King Charles III and Queen Camilla outside Victoria House to officially launch the trip.

For his part, Donald was wearing a smart suit but offered a nod to Melania's own colour palette with his choice of tie.

The Queen spent yesterday afternoon resting at Windsor Castle, having pulled out of attending the Duchess of Kent's funeral at Westminster Cathedral after suffering from acute sinusitis - but royal aides said she had recovered to greet the Trumps today.

The timings were slightly behind schedule with Trump arriving after at the planned time of 11.55am. The King arrived with the Queen in the state Bentley at 12.02pm.

Camilla was photographed wearing a vibrant sapphire blue dress, a matching coat by Fiona Clare and hat by Philip Treacy and a sapphire and diamond brooch. Kate was seen in an Emilia Wickstead dress, a hat by Jane Taylor and a feather brooch.

The President eventually emerged from his Marine One helicopter with Melania - who opted for a floor-length classic Burberry trench coat when she touched down in London yesterday - at 12.16pm, with their arrival celebrated with music.

Read More Trump's tangled history with the Royal family as he meets his 'friend' King Charles

Donald Trump is also joined by his daughter, Tiffany Trump, 31, and her husband, Michael Boulos, 28, on the trip.

Noticeably absent are Ivanka and her husband, Jared Kushner.

Trump is making history with the unprecedented second state visit to the United Kingdom with a royal return steeped in politics and the president's well-known love of pageantry.

'Trump loves pomp and circumstance, and nobody does it better than the British,' a Washington insider told the Daily Mail.

With Windsor Castle stepping in for Buckingham Palace -- now under multi-year renovation -- the Trumps are being embraced by the full royal welcome, from carriage procession to state dinner, in a show of dramatic splendor tailored to the president's taste and highly susceptible ego.

Beyond the sensitive free-speech discussions with Prime Minister Keir Starmer, Trump is expected to announce major financial commitments worth 'tens of billions' of dollars, accompanied by a delegation of American tech and financial executives.

She wore her blonde tresses in a slick bun that was largely hidden by a wide-brimmed hat in a slightly brighter purple hue

Hanging over it all will be the historic trade agreements that could fundamentally reshape post-Brexit commercial ties between the two nations and potential deals on defense and nuclear technology.

The dignitaries will participate in a carriage procession through the Windsor estate, towards the castle and have lunch in the State Dining Room.

In the afternoon Trump will tour the St. George's Chapel and lay a wreath on the Tomb of Queen Elizabeth II, a nod to her legacy.

The Trumps will then join royal family members at Windsor Castle for the state dinner later this evening where both the President and the king will give speeches.

Why Melania Trump didn't curtsy to the royals