I have uncovered something.
What you have appears to be the 'Lunario' lemon, it's a popular lemon of the Amalfi coast like 'Zagara Bianca' both are called the 'four seasons lemon'.
The 'Lunario' lemon has a purplish tone to it's young leaves and to it's flower buds (unlike 'Zagara Bianca'), it has no purple in the actual flowers themselves, the flowers themselves are just as pure white as the flowers of the 'Zagara Bianca' are. The fruit of 'Lunario' are longer in shape than the fruit of 'Zagara Bianca', yet they are still the same type of shape.
The young leaves of 'Zagara Bianca' they are a light green in color, it's flowers are pure white just like the 'Zagara Bianca' variety, and it's fruits are more round shape, than the fruit of 'Lunario'.