John Frederick III was killed in a hit and run last weekend, and on Thursday the singer appealed for the driver to come forward.
"It's like a nightmare, that we will never be able to wake from... It is with the heaviest of hearts that I say goodbye to my beautiful cousin, John Boy," she wrote. "This past Saturday October the 26th at 3am, his life was taken by a hit and run in Fort Lauderdale, FL.
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"I ask that whoever did this, has the dignity and strength to come forward. Our God is a loving and forgiving God, but I pray for justice for John Boy and closure for my family."
The "Masked Singer" judge also shared the CrimeStoppers poster, with details of the incident: police believe the suspect drove a 2009-2014 silver Hyundai Sonata, and asked the public to be on the lookout for a similar vehicle with right front end damage.