Kate was snapped alongside her husband Prince William as they paid their respects as the Queen made her final journey from Buckingham Palace.
In a doleful scene reminiscent of when Prince William and Prince Harry followed the casket of their mother as she was taken on a similar procession 25 years ago, Kate acknowledged Princess Diana as she wore the pearl drop earrings given to her as a wedding gift in 1981.
Wearing a black veil and dress, Kate also completed her outfit with a diamond and peal leaf brooch which belonged to the Queen.
The brooch features a trio of large pearls set in the centre of a pave-decorated leaf, and had been loaned to Kate by the monarch in the past.
Kate wore it at the Tyne Cot Commonwealth War Graves Cemetery in Ypres, Belgium, at a commemoration ceremony to mark the centenary of Passchendaele in 2017.
The Queen was seen wearing it on her 73rd birthday in 1999 during an official tour to South Korea.
There were emotional scenes at Westminster Hall where the Queen's coffin will lie in state until her funeral on Monday.
A video of Kate during a short service conducted by the Archbishop of Canterbury touched many as she was visibly emotional and looking to the ground.
"Beautiful inside and out. She was very close to the Queen," one said on Twitter.
"Catherine is fighting it, and only just holding it back," another said.
"Catherine is a true royal clearly heartbroken."
Prince Harry was also seen wiping tears from his eyes as the Queen's coffin arrived at Westminster Hall.
He walked with both his brother Prince William and father King Charles with Kate and Meghan Markle in tow.
"My heart breaks for [Harry]. Losing one of the main women in his life is so hard," one wrote.
"He's just a young man who misses his gran. You could see the deep affection they had for each other when they did the Invictus Games clip," another commented.
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