David Harper, 59, assumed his growing waistline was down to his love of good food and drink.
But when he lost his appetite and started suffering constipation he was sent for a scan - which revealed the huge tumour in his bowel.
The doting father is determined to live long enough to walk his daughter Leanne down the aisle at her wedding in May next year.
He said: "I like to eat and have a few beers - I just thought I was putting on a bit of weight, that I had a beer belly.
"It was only when I couldn't go to the toilet that I started to think something was wrong.
"The consultant told me the tumour was the size of a football and it was pressing down on my bowel. That's why it looked like a beer belly."
David, of Hull, East Yorks., first went to Hull Royal Infirmary in January 2016 and was diagnosed with constipation and prescribed laxatives.
When his symptoms continued to deteriorate he was sent for a scan at Queen's Centre for Oncology and Haematology in Cottingham three weeks later.
Grandfather-of-12 David said: "This time the doctor pressed my stomach and instantly had this worried look on his face.
"He sent me for a scan immediately and within 40-60 seconds of it coming back he told me that I had cancer.
"I went into some kind of trance. I couldn't think of anything. It was like I was a zombie. It was a bomb shell. My world fell apart."
He underwent surgery for bowel cancer the next day and underwent several cycles of chemotherapy.
Doctors originally gave him two or three years to live but scans last week showed that the tumor has spread faster than expected.
Daughter Leanne, 32, marries her partner James on May 18, 2018, and David is determined to give her away.
He said: "It would mean the world to me. I have always wanted to walk our five daughters down the aisle. It looks like this will be my only chance. I'm determined.
"I know it's going to be sooner rather than later when it happens. But as long as I get to that point, the wedding, I'll be happy.
"It's the proudest moment of a man's life, so I want to get to that point.
"It's just one of those things. I've got everything sorted and I'm prepared to go."
Heartbroken Christine, also 59, said: "You can't put a price on how much it would mean to Dave her down that aisle.
"We're just taking it a day at the time. We know it's coming but we're fighting to keep him here for as long as we can."
David, a training and compliance manager at SPS Security in Hull, was forced to quit work in January 2016, but remains in contact with his former colleagues who he describes as "extremely supportive."
The family is being supported by Macmillan. On Saturday, David and Christine will be holding a fundraising tombola with all proceeds going to the charity.
"They are always so cheerful and will always make you happy," said David, referring to the charity's nurses.
Christine said: "They're awesome. They've done so much to help us, from getting a specialist bed for Dave to just talking to us. The fundraiser is our way of giving something back to Macmillan."
Becky Read, Macmillan's fundraising manager for the Hull area, said: "It's very generous of David to raise money for Macmillan Cancer Support and we wish him all the best for his event on Saturday.
"As a charity, we rely on donations to help fund vital services to help people affected by cancer."
Reporting from SWNS/Ross Parry