According to this argument, Donnchadh's son and intended heir was Cailean (alias Nicholaus of Carrick), who as his son and heir, issued a charter in Donnchadh's lifetime, but seemingly predeceased him.
According to this argument, Donnchadh's son and intended successor was Cailean (alias Nicholaus of Carrick), who as his heir, issued a charter during his father's lifetime but apparently died before him.