The investigations into Andrew Mountbatten-Windsor and Lord Peter Mandelson could take more than a year, the head of the Crown Prosecution Service has said.
The former prince and Lord Mandelson face questions amid controversy over their respective links to the paedophile financier Jeffrey Epstein.
Both were arrested in February on suspicion of misconduct in public office.
They were subsequently released under investigation. Both have denied wrongdoing.
Speaking about both cases on Thursday afternoon, director of public prosecutions Stephen Parkinson said: "I really don't think that anyone should expect an early resolution of the investigation.
"It wouldn't be at all surprising if it took over a year, not because of any lack of urgency, but because of the complexity, and also the international dimension is an extra factor to be considered, notwithstanding that in some cases you can get evidence back in an hour, that's not always the case, and formal procedures have to be gone through that sometimes involve courts, and that can have significant delay, so complex, time-consuming but no lack of urgency around that case."
Mr Parkinson added that the police are "responsible for investigations" but that the CPS has been "providing early investigative advice".
The update comes after the release of a second tranche of documents relating to Mandelson's appointment as UK ambassador to the United States.
The files have fuelled renewed scrutiny of the vetting process and reignited political debate about Mandelson's links to Epstein.
Meanwhile, Andrew was pictured on Thursday with what appeared to be a large purple bruise on the right side of his face.
He was photographed while driving near his new home, Marsh Farm on the Sandringham Estate, after he was removed from his former home, Royal Lodge, in February.
Although it is unclear how the King's brother obtained the facial mark, it is understood not to be a cause for concern.
(c) Sky News 2026: Investigations into Andrew and Mandelson could take 'over a year' - as ex-prince seen with bruise on face<
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