"(Kate) was so clearly really proud of him when he came back from his speech," Chris told the publication, who explained she had been watching the duke from a TV backstage.
"They are a strong team," he added.
Behind-the-scenes photos from the ceremony were also shared to the official Duke and Duchess of Cambridge Instagram account, taken by Chris himself.
A series of black-and-white images depicted Will and Kate all smiles as they popped out from behind a curtain, as well as Will waiting backstage, and Kate with a comforting arm around her husband's waist.
The duchess donned a gorgeous lilac number while Will opted for a green, velvet suit.
"Behind the scenes at the first ever @EarthshotPrize Awards," the caption read.
Royal fans were over the moon to see the Cambridges share these candid, loved-up moments, taking to the comments to lend their support.
"How lovely to see genuine love and affection," one user wrote.
"Like a scene from a fairytale 😍," added another.
"Their romance is really regal ❤️," penned a third.
For your own fairytale love story, sign up for eharmony.