Thai-born Chamlong, 49, was found brutally murdered in a garage in west London in April 2005—only days before she was set to battle the actor in a court hearing for custody of their three children.
Allen's lawyer Sucheta Sarkas read a statement from the retired boxer and actor, saying, "I am thankful that this terrible ordeal has come to an end and I am found not guilty of the sad death of my wife.
"My thoughts at this moment are with my children that have stood with me throughout the long months that have taken to reach this moment.
"I now hope the police will reopen their inquiries and redouble their efforts to find my wife's killers."