The Oyston family has lost a High Court battle with businessman Valeri Belokon over Blackpool FC and has been ordered to buy him out for £31m.
His company, VB Football Assets, a minor shareholder in Blackpool, brought an action against the Oystons.
Mr Belokon alleged the Oystons had shown unfair prejudice against shareholders during a civil trial.
Owen Oyston, Blackpool's majority shareholder, and his son Karl, the club chairman, denied the accusations.
Mr Justice Marcus Smith ruled a "financial buyout" was the appropriate course following his findings.
Blackpool will now have to purchase the interests of VB Football Assets for £31.27m.
The Oystons were refused permission to appeal but it is open to them to apply directly to the Court of Appeal in an attempt to take their case further.
The judge ruled that an initial £10m should be paid within 28 days.
In his ruling, Mr Justice Smith said the Oystons had "abused their majority powers to the detriment" of both Mr Belokon and Blackpool FC.
In a statement, Mr Belokon said he had "always questioned the large payments" from Blackpool FC to companies owned by Owen and Karl Oyston following promotion to the Premier League.
He said: "In finding that those payments were disguised dividends to the Oyston family, today's judgment vindicates what we have all been saying.
"The judgment reveals clearly for the first time the full extent of those payments and provides transparency as to how the club has been run."
Mr Belokon said his involvement in the club was "uncertain at this time" but added: "What I am certain of is that, with the fan's support, today's judgment could mark a turning point in the club's fortunes."
Tim Fielding, honorary vice president of Blackpool Supporters' Trust, was in court along with more than 50 other fans.
Describing the mood among those present as "jubilant", he said: "It's a massive game changer. The figures that they [the Oyston family] would have to pay to keep hold of the football club are huge.
"We are hoping that this will see regime change. I think the reality is they will have to find a buyer for the club. This is what we have been fighting for for the last four years, and it's come to fruition."
Lawyers for VB Football Assets complained both Mr Belokon and his nominated directors were excluded from key decisions, information and a share of profits.
The Oystons gave evidence that all financial transactions were conducted in an open and transparent manner.
Mr Justice Smith said there had been "unfair prejudice".
Latvian Mr Belokon, who resigned as a director of the club in August, accused the Oystons of improperly extracting tens of millions of pounds from the Lancashire club's funds after it enjoyed a "jackpot" when winning promotion to the Premier League in 2010.
He claimed the family had treated the club as "their own personal cash machine" and said he felt betrayed by their actions.
The claim was also brought against Blackpool FC Ltd itself and Blackpool FC (Properties) Ltd, a company with Oyston family links and formerly known as Segesta.