Unknown letter

At 1930,

A man named peter,who meet a girl called jenny during the train travel at london.

While traveling they became very close eachother.

After that peter used to write letter regularly to jenny's address.

Peter also getting reply letter regularly,months gone,years gone they writing letter continuously to jenny also getting reply.

It continuous till death of peter at 1980,but they never meet once again.

Nobody knows who will writing reply letter,but it continues till peter death.