A 50-year-old man was charged with murder for fatally stabbing his younger brother inside their apartment at a Bronx housing project after investigators found he had invented a false story to cover his tracks, police sources said Saturday.

Dennis Martinez originally told police that a trio of thugs stabbed him and his brother Jorge Montanez inside the Castle Hill Houses on Seward Avenue in Castle Hill during a dispute at around 6:40 a.m. on Friday, sources said.

Montanez was knifed in the in the torso, back and leg inside the first floor apartment he shared with Martinez, sources said.

Montanez died at Jacobi Hospital about an hour after the stabbing.

Martinez also suffered a stab wound to his right thigh. It’s unclear how he got that wound, sources said.

Martinez has about a dozen prior arrests on his record and Montanez has nine prior arrests, sources said.

It was not immediately known what sparked the fatal knife fight.