That is never stated and wikipedia says its an old friend.
You’re fucking retarded.
A sequel to Rambo (2008), it is the fifth installment in the Rambo franchise and co-stars Paz Vega, Sergio Peris-Mencheta, Adriana Barraza, Yvette Monreal, Genie Kim, Joaquín Cosío, and Oscar Jaenada. The story follows Rambo as he travels to Mexico to save his
niece, who has been kidnapped by a Mexican cartel.
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Rambo: Last Blood - Wikipedia