Proper to welcome a Trojan king (5)
I believe the answer is:
priam
'trojan king' is the definition.
(I've seen this before)
'proper to welcome a' is the wordplay.
'proper' becomes 'prim' ('prim' can be similar in meaning to 'proper').
'to welcome' indicates putting letters inside (in sense of 'inviting in').
'prim' placed around 'a' is 'PRIAM'.
(Other definitions for priam that I've seen before include "Old king" , "Father of Paris in Troy" , "Trojan king" , "The last king of Troy, in Greek mythology" , "Old man of Paris" .)