Michael Keane, 20, was on Bondi Beach in Sydney when he was photographing the sunrise with his camera.
The university student didn't realise at the time that he was taking pictures of the proposal. He later posted them on Reddit.
Keane recalled: "I saw the couple's silhouette on the cliff, so I started taking pictures with them in it because I thought it would be cool in the pictures.
"It wasn't until I got home and was looking through my camera that I realised, 'Holy crap, he is down on one knee in this one'."
The two people photographed were later identified as Steven McConnell, 32, and Irene Kotov, 29.
The couple contacted Keane and now intend to frame the pictures.
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