Updated

In a scathing open letter to LeBron James' onetime diehard fans, the majority owner of the Cleveland Cavaliers is blasting the NBA superstar, calling his decision to play for the Miami Heat a "bitterly disappointing" blow and a "shocking act of disloyalty from our home grown 'chosen one.'"

Dan Gilbert also personally guaranteed that the Cavaliers will win an NBA championship before the "self-titled former 'King' wins one" with the Heat.

"You can take it to the bank," reads Gilbert's letter, which has been posted on the team's Web page on nba.com. "If you thought we were motivated before [Thursday] to bring the hardware to Cleveland, I can tell you that this shameful display of selfishness and betrayal by one of our very own has shifted our 'motivation' to previously unknown and previously never experienced levels."

Gilbert said James' decision to leave Cleveland after seven seasons -- and without a coveted NBA title -- sent the "exact opposite lesson of what we would want our children to learn."

"The self-declared former 'King' will be taking the 'curse' with him down south," Gilbert wrote of Cleveland's so-called curse against winning sports championships. "And until he does 'right' by Cleveland and Ohio, James (and the town where he plays) will unfortunately own this dreaded spell and bad karma."

Cleveland fans "simply don't deserve this kind of cowardly betrayal," Gilbert's letter continued.