### Clue: Queen goes past prince, not unknown one, in jump jet (7)
### Answer: HARRIER 
 ### Explanation: Definition: jump jet
  ER(the Queen, $$E$$lizabeth $$R$$egina) **placed after**(goes past) [HARR{"Harry"(prince) **minus**(not) "y"(in algebra, one of the symbols used to represent an unknown quantity)} + I(Roman numeral for one)].
Answer: The awesome vertical take-off and landing jet fighter plane.