Kate was accompanied by her children Prince George, nine, and Princess Charlotte, seven, as she made her way inside to join over 2,000 attendees.
In a show of support, the mother-of-three was spotted holding hands with Charlotte as they entered Westminster Abbey.
WATCH: Kate holds Charlotte's hand as they arrive at Queen's funeral
In keeping with the mourning dress code, Kate opted to wear a flattering black gown with a matching statement hat. The 40-year-old teamed her outfit with pearl earrings and styled her chocolate tresses in a chic updo.
seven-year-old Charlotte walked by her mother's side
Dressed in military uniform, Prince William donned his RAF No1 uniform complete with his garter sash and RAF pilot wings.
Kate could be seen holding Charlotte's hand
The two young royals will walk through the church in procession behind the late monarch's coffin as it is carried by the military bearer party.
Also in attendance were the likes of the Duke and Duchess of Sussex, the Princess Royal and the Earl and Countess of Wessex.
The Prince and Princess of Wales travelled with a police escort
Various heads of state, prime ministers and presidents, European royals and key figures from public life moreover gathered to celebrate the life of Her Majesty.
Following the funeral, the Queen's coffin will travel in procession from Westminster Abbey to Wellington Arch. From Wellington Arch, the coffin will travel to Windsor and once there, the state hearse will travel in procession to St. George's Chapel, Windsor Castle. A committal service will then take place in St George's Chapel.
The late monarch passed away "peacefully" at her Balmoral residence
Her Majesty will be laid to rest at the King George VI memorial chapel, the resting place of her parents and sister, King George VI and Queen Elizabeth The Queen Mother, and Princess Margaret.
Once the funeral has taken place, the Queen's late husband Prince Phillip will be moved from the Royal Vault of St George's Chapel to Windsor Castle's King George VI Memorial Chapel, where he will be laid alongside his lifelong partner.
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