Aintree, UK - A father of three was devastated when a vet gave his Labrador Bella a stark health diagnosis. But then, he learned that he, too, was battling the same potentially fatal disease.

Simon O'Brien and his dog had similar symptoms: they felt tired all the time, were constantly thirsty, and rapidly losing weight. During examinations last year, both were diagnosed with kidney cancer.

Convinced that his days were numbered, the 48-year-old began planning his own funeral and arranging his affairs, even writing letters to his children Ivy (27), Callum (18), and Niamh (14) to open on big occasions in the future.

But thankfully, he made a huge turnaround: earlier this year, O'Brieny went into remission after he had his kidney removed in a seven-hour emergency operation, according to British tabloid Metro.

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Yet, he and his family were crushed when they were told the same operation was too risky for their eight-year-old pup, whose condition is now terminal.

That's why the project manager, who lives in the UK with his wife Ruth and their kids, now spends what precious time Bella has left with her.

"She is my best friend and is so much more than a dog to us, she is family," O'Brien said.

Medical director Dr Laura Chapman told the outlet: "This is such a sad situation, to have Simon and Bella diagnosed with the same type of cancer at the same time is something I have never heard of in my medical career.

"The chances of a dog getting this relatively unusual cancer at the same time as her owner are around a million to one."

When Bella started losing weight, sleeping more, and drinking a lot of water in May 2022, alarm bells went off, O'Brien said, adding that before that she had always been cheerful and enjoyed playing with the kids.

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She also used to groom herself a lot, but suddenly the dog stopped doing that and tucked her tail between her legs. It "was unusual, so we knew something was wrong," the owner said.

After various tests, a veterinarian confirmed Bella's kidney cancer and said she only had "months to live."

O'Brien received his own diagnosis of the same disease a few months later in October, when he began feeling exhausted after routine workouts as an avid runner.

"It was like a bolt out of the blue and having two cancers in the family at the same time has been awful."

Luckily, he is now on the road to recovery.

Thanks to medication, Bella is living longer than originally expected. The O'Briens take her to the beach as often as possible because she loves the waves, where they make the most of their time together.