The Duke of York’s legal team first approached Gallagher in the wake of Prince Andrew’s Newsnight interview with Emily Maitlis.
He is a leading crisis-management expert who helped clear clients falsely accused in Operation Midland, an investigation into allegations of abuse by high-profile figures.
Prince Andrew’s legal team includes extradition lawyer Clare Montgomery QC and Blackfords partner Gary Bloxsome.
A formal working arrangement with Gallagher began in January and PRWeek understands he has brought in two colleagues to work on the case.
A source told PRWeek: “Mark understands that there are always two sides to a story – and Operation Midland was a classic example of exactly that. He believes that will become more than apparent in this case, too, and has no doubt that the Duke will be exonerated.”
Prince Andrew has faced mounting pressure to co-operate with the FBI and US prosecutors in their investigation into his former friend Jeffrey Epstein, the US financier and convicted sex offender who died in custody while awaiting trial on sex trafficking charges.
The Duke has vehemently denied allegations that he had sex with one of Epstein’s victims, Virginia Roberts Giuffre, when she was 17.
Gallagher brings a strong track record of helping to exonerate high-profile individuals.
His most famous case involved several politicians, including former prime minister Sir Edward Heath, Lord Edwin Bramall, former Conservative MP Harvey Proctor, and Lord Brittain, who were falsely accused of child abuse – claims that led to the Metropolitan Police's Operation Midland investigation.