Did not make up missed fasts before arrival of following Ramadhaan due to negligence

What is the ruling regarding the one who did not make up the missed fasts of Ramadhaan until the arrival of the following Ramadhaan, whilst he did not have a[n Islaamically valid] reason? Is it sufficient for him to repent [to Allaah] in addition to making up [the missed fasts] or is he [also] required to make an expiation (kaffaarah)?