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Stabbed to Death

Seattle Mariners outfielder Greg Halman was stabbed to death early Monday morning in the Netherlands ... and cops say his own brother has been arrested as a suspect.

Cops were called to an apartment in the city of Rotterdam early this morning where they discovered 24-year-old Halman bleeding from a stab wound. Officers were unable to revive him.

Cops later arrested Halman's 22-year-old brother in connection with the murder.

Halman has played sparingly for the Mariners, appearing in 44 games over the past two seasons.

Law enforcement tells TMZ ... Greg and his brother had been living together at the apartment -- and a woman was staying with Greg at the time of the murder.

Cops say the woman was the person who called authorities and identified Greg's brother as the murderer.