Bella, a Labrador cross, was bought by David Richardson from the RSPCA, 26 years ago when she was three years old.
She had lived with Mr Richardson, 76, and his partner Daisy, 81, since 1982 in Clay Cross, Derbyshire.
But she was put down on Saturday following a heart attack while on holiday with the couple.
Until Bella the record for the oldest dog was held by Butch, a 28-year-old from America who died in 2003, according to the Guinness World Records. Officially, the oldest ever dog was Bluey, a sheepdog from Australia, who lived to 29.