Lulu, named for the Scottish singer, was the runt of her litter, photographed here by Paul Macnamara in January 2010.
As her sister and two brothers grew, it was obvious at nine weeks, and only four inches long, Lulu had stopped growing.
She makes up for a tiny size with an enormous personality. She sleeps much of the day on a hot water bottle, but when the sun goes down she becomes active and eager to run all over her owner's bed.
Dwarfed chihuahuas sell for huge amounts of money but really can't be bred. They're never really healthy and will cost a fortune in vet bills if they're to live a decent life. So the 76 year old breeder, Jean Tindall of West Yorkshire, has decided never to sell her, but commit the family to Lulu's longterm care.
"I've had a few inquiries about Lulu because she's such a wonderful cute little thing. But to me she is priceless. I would never sell her. She's a little star and loves all the attention she gets."
For comparison, the famous chi-yorkie Tilly, declared in 2009 to be Britain's smallest dog, reached eight inches, twice the size of Lulu who makes even the smallest small dogs look big.
It'll have to wait until she's a year old to assess whether or not Lulu is the smallest dog in the world. She seems to have stopped growing but she might put on a bit more size.