The collection included 77 pieces of gold and gemstone jewellery, including crowns, amulets, belts, and earrings. One item of note was a solid gold bowl believed to be dated to the 11th century.
The items were discovered as part of an investigation into British antiques smuggler Douglas Latchford.
Latchford, who was a renowned expert and dealer in Cambodian and Indian antiquities, died in 2020 while awaiting trial in the US for charges relating to smuggling.
Brad Gordon, the head of Cambodia's investigative team, told the BBC that he became emotional when first shown the jewellery.
"I was driven by a representative of the Latchford family to an undisclosed location. In the parking lot was a vehicle with four boxes inside. I felt like crying. I just thought - wow - the crown jewels of ancient Cambodian civilization packed into four boxes in the back of a car," he said.
According to reporting from the ABC experts believe many of the items recovered were looted during periods of war, including in the 1970s when the country was under the rule of the Khmer Rouge.
Cambodian minister Phoeurng Sackona said: "The repatriation of these national treasures opens a new era of understanding and scholarship about the Angkorian empire and its significance to the world."
She added: "We consider such returns as a noble act, which not only demonstrates important contributions to a nation's culture, but also contributes to the reconciliation and healing of Cambodians who went through decades of civil war and suffered tremendously from the tragedy of the Khmer Rouge genocide.”
The collection has been returned to Phnom Penh and is scheduled to go on display in the country's national museum.
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