Under the will, the $1.4 million was to be used to generate an income for his wife and, following her death, to be distributed among his sons.
But it was Mr Dean's choice of his financial planner, Mr Moyle, as executor which put his will on a course for the High Court.
After years of trying to get information about the estate and how the money was being invested, his sons turned to the court process to obtain the information free.
A High Court judgment revealed the value of the estate had dropped by $230,000 over 10 years - and Mr Moyle's firm New Zealand Financial Planning was charging more than $1000 a month as a portfolio monitoring fee.
It also showed an unauthorised payment of $52,000 out of the capital of the fund to Mr Dean's wife, also an executor of the will. His wife, now Wendy Russell, was meant to be paid out of the estate's earnings - but the payment was made in a year when a property investment lost $70,000 and earnings were down.
Justice Murray Gilbert found Mr Moyle had "persistently failed over many years" to provide information to Mr Dean's sons even though they were entitled to it and it was available.
He found the sons - Allan, Kerry and Brett - had tried for seven years to find out the state of their father's estate without success.
Last year, lawyers acting for the sons filed court action.
Mr Moyle produced the information, but the court ordered him to pay court costs. Justice Gilbert said the costs were incurred "solely as a result of Mr Moyle's conduct", noting his "failure to perform his duties as a trustee" by providing information about the investments.
Mr Moyle said he disagreed with some of the facts in the judgment but accepted he had not kept Mr Dean's sons informed.
He said he believed he was "piggy in the middle" in a domestic dispute between Mr Dean's sons and their stepmother.
But he said he had distanced himself from the investments, which had performed in all years except the last. The fees - more than $100,000 in seven years - were standard and reflected the cost of managing a $1.4 million estate.
"No one is out of pocket. Everyone has been paid," Mr Moyle said.
"I acknowledge in hindsight I should have provided more information to the capital beneficiaries."
Kerry Dean said he and his brothers took the case to court because they felt shut out of the estate.
"We've gone for years and years without hearing anything. You'd think people would follow the rules."
It emerged during Herald inquiries that Mr Moyle is no longer with NZ Financial Planning, resigning his role as adviser and director days ago.
But he remains a shareholder in the company he started almost 22 years ago, through which he built his profile as a businessman while becoming increasingly involved in community projects.
NZ Financial Planning general manager Craig Dealey said the company had only recently learned of the court case, shortly after Mr Moyle resigned. "We didn't like what we read there and certainly didn't condone how it was handled."
He said some clients asked advisers to be executors of their wills. The company managed it by keeping them separate from investments made with the estates and keeping a register - steps which were followed in this case.
The court action was unknown but should have been disclosed.
"We only found out about this in the last couple of weeks. It hadn't been notified to the directors before that by Greg."
Mr Moyle is on the Auckland Council's Waitemata Local Board and has previously served as an Auckland City councillor.
He has also been chairman of the Mount Albert Grammar School board of trustees and president for the school's old boys association.
Other positions he has held include as a trustee for the Leukaemia, Blood and Cancer Foundation, a director of Radio Lollipop and a trustee of the Ranfurly Veterans Home.
A spokeswoman for the Financial Markets Authority said the authority had received a previous complaint about Mr Moyle in 2011 and he had since been subject to a monitoring visit from FMA. There had been no complaint about this case.
