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A gnarly fight broke out in front of "So You Think You Can Dance" star Joshua Allen 's open casket over the weekend -- and it's caused tension among his family.

Check out the video circulating online -- you can see a young female leaning over the casket, when all of a sudden, an older woman pounces on her to pull her back ... and an all-out brawl breaks out.

The shocking situation took place at his Texas funeral Saturday and has drawn a divide between each side of Joshua's family ... 'cause his father, Eddie Powell , tells TMZ the woman leaning over the casket was Joshua's girlfriend! He alleges members of Joshua's mother, Angela Tolbert 's, side of the family assaulted her while she was simply trying to place a note on his body and kiss him goodbye. Getty

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