Judge Mitchell Beckloff made the ruling on Wednesday after considering a letter submitted by singer Diana Ross, who was a close friend of Michael'.
In the letter, the 68-year-old reportedly expressed her support for TJ, saying she believes he has good intentions in caring for the three children.
The Judge also asked Katherine’s attorney if she had being unduly influenced to agree with the co-guardianship, presumably in light of the ongoing Jackson family feud.
"Absolutely not! Ms Jackson is well informed, makes her own decisions and wholeheartedly supports this arrangement,"replied the attorney.
He told TJ to be wary of the ongoing rift amongst Jackson family members — asking him to make sure the kids are not negatively affected.
The 34-year-old was appointed temporary guardianship last month when Katherine went "missing" during a visit to relatives in Arizona.
But not all ran smoothly in court.
A woman claiming to be Michael’s cousin, Debra Jackson, arrived with her adult son Anthony and submitted a letter of concern about appointing TJ co-guardian.
She said Michael helped raise Anthony after his own father died and that she and her son had been "cruelly" cut off from Prince, Paris and Blanket.
Judge Beckloff considered the letter before handing down his final decision.
"It’s clear to me that the children have a very strong, loving relationship with TJ and that they love the grandmother very much," he said.
If either TJ or Katherine is unable to serve as co-guardian, the other would become the kids' sole carer.