Nicola Sturgeon has been arrested as part of an ongoing police probe into the SNP's finances.
Scotland's longest serving First Minister, who stepped down in March, was taken into custody today and is being questioned by detectives, Police Scotland said.
A statement from Police Scotland said: "A 52-year-old woman has today, Sunday, June 11, been arrested as a suspect in connection with the ongoing investigation into the funding and finances of the Scottish National Party."
Police are probing the spending of around £600,000 earmarked for independence campaigning, as part of Operation Branchform.
A spokeswoman for Ms Sturgeon said the former SNP leader was cooperating with the investigation.
Teachers, civil servants and train drivers walk out in biggest strike in decadeThe spokeswoman said: "Nicola Sturgeon has today, Sunday June 11, by arrangement with Police Scotland, attended an interview where she was to be arrested and questioned in relation to Operation Branchform.
"Nicola has consistently said she would cooperate with the investigation if asked and continues to do so."
It comes after Ms Sturgeon's husband Peter Murrell, a former SNP chief executive, was arrested in April.
Mr Murrell and MSP Colin Beattie, who was SNP treasurer at the time, were both released without charge pending further inquiry.
Officers raided Ms Sturgeon and her husband's home in Uddingston, outside Glasgow, in April, with a police tent erected in their garden.
Police also searched the SNP headquarters in Edinburgh and seized a luxury campervan from outside a house in Dunfermline, Fife, understood to be the address of Ms Sturgeon's mother-in-law.
Mr Murrell, 58, is the former chief executive of the SNP, who quit his role following a separate row over party membership figures.
The news will pile further misery on Ms Sturgeon's successor Humza Yousaf, who is battling to turn around his party's fortunes amid a deepening crisis.
Shadow Scotland Secretary Ian Murray said: “This is a deeply concerning development and the Police Scotland investigation must be allowed to proceed without interference.
“For too long, a culture of secrecy and cover-up has been allowed to fester at the heart of the SNP.
Richard 'shuts up' GMB guest who says Hancock 'deserved' being called 'd***head'“The same culture that leads to police tents in front gardens created the deeply dysfunctional government that is currently failing Scots.
“Humza Yousaf must urgently come clean on what he knows - the people of Scotland deserve answers.”
Ms Sturgeon stood down as First Minister and SNP leader in March after nearly nine years at the top of Scottish politics.
Her shock resignation came after a string of political rows appeared to take its toll, including increasing divisions in the party over its strategy on independence and transgender rights.
Speaking in February, she said she was not quitting due to "short term pressures" and instead blamed the "brutality" of life in frontline politics.
Since taking over from Alex Salmond after he failed to secure Scottish independence in the 2014 referendum, Ms Sturgeon became one of the best known - and most divisive - figures in UK politics.
She continues to be the MSP for Glasgow Southside.