But in an April 2018 judgment Justice Christine Gordon dismissed his claim and ruled Reid had gifted the $1.7m to his son.
So Reid took the case to the Court of Appeal last month, which today released its decision.
"In our judgment the evidence before the court is insufficient to support the finding Mr Reid intended to gift $1,700,000 to Mr Castleton-Reid," Justice Geoffrey Venning said, giving reasons for the panel of three judges.
"Mr Reid did not intend to immediately vest the $1.7m to the benefit of Mr Castleton-Reid ... Rather, the evidence supports a conclusion that, at most, Mr Reid may have intended Mr Castleton-Reid to inherit the balance of the money in the Trading Account on his death."
The judges allowed the appeal and costs ordered in Castleton-Reid's favour were set aside.
The case will now return to the High Court for a further hearing to determine the parties' respective interests in the balance of the money from the trading account.
Court of Appeal judgment also described Reid's mixed success in his financial endeavours over the course of his life.
He and his brother established a successful building business, Reidbuilt Homes Ltd, which they sold to Fletchers in 1984 for $1m.
However, since then, Reid's business ventures have not been as successful and more recently he has been bankrupted twice, in August 1999 and May 2003.
He said he now has no assets and substantial debt, while his sole income is his superannuation, the Court of Appeal decision reads.
Reid's wife, Esme, died in November 2018, while the couple were living in the Castle, which was held in her name.
The source of the funds for the trading account was a term deposit of $1,750,000 with Kiwibank which had been held in the joint names of Reid and his wife.
Castleton-Reid was the principal beneficiary under his mother's will and codicil, while her husband was named as executor of her will, but was not a beneficiary.
Castleton-Reid's sister, Dee-Ann Castleton-Reid, received furniture, books, jewellery and other chattels, as well as the right to live in the Castle with her brother - which she chose not to do.
Her brother was also left another property and two vehicles, one of which was a classic car, a bequest of $50,000, and the residue of his mother's estate. The residue comprised shares in Air New Zealand and Auckland Airport.
"Apparently, the catalyst for Mr Castleton-Reid closing the account and terminating Mr Reid's access was his discovery, in late April 2010, that a mortgage had been registered against the title to the Castle to support a bond issued in favour of Mr Reid," the Court of Appeal judgment reads.
"Mr Castleton-Reid took the view his father had been dealing with the property from his mother's estate (which Mr Castleton-Reid was entitled to as beneficiary), as if it was own."
The decision said Reid had taken dividends earned in the shareholding account and had used the Castle as security for his personal debts when he was only registered on the title as an executor.
"For those reasons [Castleton-Reid] says he lost trust in his father and closed the trading account," the judgment reads.
