This is no stunt to Anderson Silva ... the MMA legend says he's been training his ass off for his June 19 fight against Julio César Chávez Jr. -- preparing for an all-out war.
We broke the story ... 46-year-old Silva is all set to fight 35-year-old Chávez Jr. at Jalisco Stadium in Guadalajara, Mexico.
Silva was known as one of the top strikers during his UFC career -- but he hasn't taken a pro boxing match since 2005 ... while Chavez is 52-5-1 as a pro and scored a victory over Jeyson Minda in his latest fight back in Nov.