I might add just because you are a descendant of royalty,even direct descendant of a king, that does not necessarily make you royalty. If so a good part of the Anglo Saxon people of the American South would be royalty. Ask any professional genalogist.
The Borghese do have valid noble titles and to "upgrade" this nobility to royalty denigrates the importance of the nobility.

A prince may be a member of a royal or highly noble family, sharing their title with seveeral relatives in similar position. The Borghese are a highly noble family. I understand the young man in question has stated 2 or 3 times in interviews that the Borghese line is not royal but nobility. He is not one of the Savoia.
Now important nobles are frequently seen as far more significant than royalty from the petty kingdoms of the 19th century and beyond.
The Borghese are Papal nobility. Don't confuse them with the Borgias. The Borghese line as a noble family began when Paul Paul V bestowed a title on a nephew back in the 1600s.
When Garibaldi overthrew the Papal States the latter part of the 19th century and united Italy into one nation,he conveyed the title of King on the Duke of Savoy (Savoia). The Savoy monarchy is not recognized in Italy.
However, the Borghese get their titles from the Papacy not the government of Italy. Some of the Papal nobility can trace family lines back before Christianity to the Roman Republic.