Tusked beast smuggled back with prince (7)
I believe the answer is:
narwhal
'tusked beast' is the definition.
'smuggled back with prince' is the wordplay.
I cannot quite understand how this works, but
'with' could be 'w' (abbreviation) and 'w' is present in the answer.
'prince' could be 'hal' (I've seen this before) and 'hal' is present in the answer.
This explanation may well be incorrect...
(Other definitions for narwhal that I've seen before include "Warn Hal there's a whale here" , "Sea creature with a long spiral tusk" , "Cetacean with large tusk" , "Small Arctic whale" , "Tusked sea mammal" .)