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.

Eddie adds .. “She was his heart. She was trying to help him get mental health treatment when the police got involved instead.” He also says she had hopes of marrying him.

Eddie further claims the woman received “direct permission” from Joshua’s mother to attend his services, adding … “She came in peace. She showed nothing but grace, patience, and love.”

At least one person who attended the funeral has said online that the woman who received the brutal beating is actually his ex-girlfriend. TMZ has reached out to several family members on his mother’s side for clarification … so far, no word back.

TMZ has also reached out to the Fort Worth Police Department for comment … nothing back yet.

We broke the news … the 36-year-old professional dancer was struck and killed by a train on the last day of September.

His father — who says he did not attend the rest of his funeral services due to the violent altercation — tells TMZ Joshua struggled with mental health issues for a long time before his death.

Joshua rose to fame after winning “So You Think You Can Dance” Season 4, where the late Stephen “tWitch” Boss placed 2nd. He went on to star in 2010’s “Step Up 3D” and 2011’s “Footloose” remake.