kate middleton
Prince WIlliam, The Duke of Cambridge and Catherine, Duchess of Cambridge talk with Matthew Barzun (R) , US Ambassador to London after signing a book of condolence for the Orlando mass shooting victims while at the US EmbassyPhilip Toscano - WPA Pool/Getty Images

The Duke and Duchess of Cambridge visited the US Embassy in London today (14 June) to sign a book of condolence for the victims of the Orlando mass shooting.

A sombre Prince William looked on as his wife, Kate Middleton, signed the book on a large wooden table decorated with white roses in front of an American flag backdrop. The 33-year-old also added his signature to the book before the couple greeted staff at the embassy with warm smiles.

Regarding the deadliest lone gunman shooting in American history, and the nation's worst terror attack since 9/11, their message read: "With our deepest condolences and with our thoughts and prayers to all those affected. William, Catherine."

The pair were welcomed by US Ambassador Matthew Barzun and were also spotted chatting with deputy chief of mission, Elizabeth Dibble, as they viewed a model of the US Embassy in a glass case.

The Duke and Duchess arrived at the London Chancery Building – which houses the embassy – at 11am and stayed for approximately 15 minutes. Kensington Palace's official Twitter account posted a tweet about the appearance: "The Duke and Duchess of Cambridge will briefly visit the US Embassy this morning to sign a book of condolence for the Orlando nightclub shooting."

kate middleton
Duchess of Cambridge signs a book of condolence for the Orlando mass shooting victims as Prince WIlliam, The Duke of Cambridge looks on at the US EmbassyPhilip Toscano - WPA Pool/Getty Images

Appearing in stark contrast from her bold appearance in scarlet red for the Queen's Garter Day Service on Monday (13 June), where she donned a custom made Catherine Walker coat and dress, Middleton, 34, wore a knee-length monochrome print dress with a blazer and black court shoes, keeping her hair and make-up simple as a mark of respect.

kate middleton
Prince William, The Duke of Cambridge and Catherine, Duchess of Cambridge talk with Matthew Barzun (R) , US Ambassador to London after signing a book of condolence for the Orlando mass shooting victimsPhilip Toscano - WPA Pool/Getty Images

It has been confirmed that 49 people were shot dead at the gay nightclub, Pulse, in Orlando. A subsequent 53 people are thought to be injured from the attack carried out by 29-year-old Omar Mateen, who was later killed in a gunfight with the police.

kate middleton
Catherine, The Duchess of Cambridge chats with Elizabeth Dibble, deputy chief of mission, as they look at a model of the new US EmbassyPhilip Toscano - WPA Pool/Getty Images

President Obama said of the tragic events: "We know enough to say that this was an act of terror and act of hate." The Queen also paid tribute to the victims yesterday in a statement citing: "Prince Phillip and I have been shocked by the events in Orlando. Our thoughts and prayers are with all those who have been affected."

kate middleton
Catherine, Duchess of Cambridge meets staff after she signed a book of condolence for Orlando mass shooting victimsPhilip Toscano - WPA Pool/Getty Images