Police Scotland's chief constable is being investigated by the police watchdog over claims of gross misconduct.
The Police Investigations and Review Commissioner (Pirc) announced it would be reviewing an allegation made against a senior officer on Wednesday.
No information has been given over what the allegation is about, but if a serious breach of standards is found, Chief Constable Phil Gormley could face dismissal.
Chief Constable Phil Gormley said: "I can confirm that today I was informed by the Pirc that I am the subject of a conduct investigation.
"I am co-operating fully with the Pirc and will provide all necessary assistance to bring this matter to a timely and satisfactory conclusion.
"In fairness to others who may be involved, it is not appropriate for me to comment further at this time.
"I would like to stress that I remain focused on leading Police Scotland, ensuring that we continue to serve and protect the people of this country."
It was sparked after a complaint was made against the chief constable to the Scottish Police Authority (SPA).
After receiving an allegation against a senior officer, the body decides whether it should be referred to the independent watchdog for investigation.
An SPA spokesman said: "The SPA can confirm an allegation against the chief constable has been referred to Pirc for their investigation.
"However, consideration of complaints and conduct issues are confidential while being progressed, and the SPA has a policy of not commenting on individual cases."
A spokesman for the Pirc said: "Following a referral by the SPA, the commissioner has assessed that the conduct which is the subject of the allegation would, if proved, amount to gross misconduct.
"Once the investigation is concluded the commissioner must determine whether, in the investigator's opinion, the senior officer has a case to answer in relation to the misconduct allegation.
"The commissioner must submit a report to the SPA containing a summary of the evidence and the investigator's opinion on whether the allegation should be referred to a misconduct hearing.
"Where the authority determines that there is a case to answer for either misconduct or gross misconduct, it must refer the misconduct allegation to a misconduct hearing.
"As this is a live investigation it would be inappropriate to comment further at this time."
Scottish Liberal Democrat leader Willie Rennie said: "This is an incredibly serious announcement.
"Phil Gormley was brought into Police Scotland to steady the ship and is now the subject of a conduct investigation.
"This announcement will have serious implications which will need to be considered over the next few days. I will make a further statement in due course."
Mr Rennie called for Mr Gormley to step aside from his role while the investigation takes place.
He said: "These allegations of gross misconduct are incredibly serious and require a thorough and prompt investigation.
"For that investigation to be conducted effectively it will be necessary for the chief constable to seek leave of absence from his post. Any leave of absence should not imply acceptance of guilt.
"Previous cases in Scotland and other parts of the UK have set a precedent, where the person who has been under investigation has temporarily stepped aside."
Scottish Labour's justice spokeswoman, Claire Baker, said: "All allegations must be fully investigated and I'd urge the Police Investigations and Review Commissioner to be as transparent as possible.
"With the most senior police officer under investigation, it is vital that whatever the outcome the public maintains confidence in Police Scotland."