"In a scene echoing the horror movie Alien, Gavin staggered into his GP‚Äôs surgery bleeding from his belly button.
His stunned GP Dr Joe Santos said: ‚ÄúIt was like something from Alien. I didn‚Äôt believe Gavin when he said something was coming out of his belly button until I saw him.
Medics said the growth was a parasitic twin ‚ÄĒ Gavin‚Äôs identical brother who died in the womb early in their mum‚Äôs pregnancy.
The 4cm foetus then became embedded in Gavin‚Äôs tissue and stayed in his stomach for the next 30 years.
There are just a handful of cases worldwide ‚ÄĒ with the majority reported in Asia.
Former firefighter Gavin, of Witney, Oxfordshire, said: ‚ÄúFour hospital doctors had previously examined me and were all puzzled by the lump.
‚ÄúSome thought it was a cyst, others an in-grown hair.
‚ÄúThen one said it could be my undeveloped identical twin that I absorbed at a very early stage. I feel absolutely fine now but it has not sunk in yet that I could have had a twin brother. I have him in a jar at home and I call him little Gav. I haven‚Äôt told many people. I feel like a bit of a freak.‚ÄĚ
Gavin‚Äôs amazing ‚Äúbirth‚ÄĚ is like the scene from 1979 movie Alien ‚ÄĒ where a monster explodes from an astronaut‚Äôs chest. The 6ft plumber‚Äôs real-life ordeal followed a month of excruciating pain.
He revealed: ‚ÄúAt first I thought I had been stung by something due to the burning pain in my belly button.
‚ÄúBut there was no sign of anything on the skin. Then I felt a large lump just above my navel, which was so painful that I nearly passed out.
‚ÄúI couldn‚Äôt sleep and made an emergency appointment with the GP the next day.
‚ÄúThere was a red patch around the area which was hot to the touch. Dr Santos felt it and said it was a hernia.‚ÄĚ
Gavin, who has four children with wife Kate, then spent a week in and out of hospital. An operation at Oxford‚Äôs John Radcliffe Hospital was cancelled at the last minute and Gavin went home.
But he later felt a stabbing pain near his belly button.
Lifting his shirt, he saw that he was bleeding as the lump pushed through his skin.
Gavin, who drove himself to his local surgery despite the shooting pain, added: ‚ÄúI had the seat tilted right back and gritted my teeth.
‚ÄúDr Santos was shocked at the sight of what came out.
‚ÄúHe told me: ‚ÄėI have amputated limbs and done all sorts, but I have never seen anything like this in my life.‚Äô
‚ÄúHe put it in a jar and put a surgical patch over my navel, then got straight on the phone to the emergency department.‚ÄĚ
Dr Santos added: ‚ÄúThis is incredibly rare. Gavin‚Äôs weight has changed recently so that is why it might have pushed through. But otherwise he is fit and well and happy that he has his little friend.‚ÄĚ
Sparknotes: Dude feels pain in stomach, doctors say that it's a cyst or ingrown hair, but another doctor said that it was his twin. He feels a burning pain, drives himself to the emergency room, and then he sees his unborn twin pop out from inside of him. He keeps it in a jar and named it "Little Gav".