Sophie, Duchess of Edinburgh's police motorcyclist could face criminal charges over the death of an 81-year-old woman, the Independent Office for Police Conduct said.
Helen Holland died in May after being hit by the officer’s vehicle which was part of the royal’s police escort.
She fought for her life for two weeks before passing away, her heartbroken son confirmed.
IOPC director Amanda Rowe said: "Our thoughts remain with Ms Holland's family, friends and everyone affected by her death.
"This is a tragic incident and it is important that we carry out a thorough, independent investigation to establish the full circumstances, which will include the actions and decision-making of the officer under investigation.
"We have been in regular contact with Ms Holland's family and we will keep them updated as our investigation progresses.
"At the end of our investigation, we will decide whether to refer the matter to the Crown Prosecution Service for a charging decision and whether the officer should face disciplinary proceedings."
Sophie said at the time she was "deeply saddened" by the incident.
Ms Holland was "thrown 40 feet across the road" after being struck by the motorbike, an eyewitness claimed at the time.
She was hit at a junction in Earl's Court, west London, on the afternoon of May 10.
Announcing her death, her son Martin told the BBC that she fought "for her life for nearly two weeks... but irreversible damage to her brain finally ended the battle".
She sustained "multiple broken bones and massive internal injuries" after being hit while using the "safe route of [a] pedestrian crossing", he added.
Martin said he did not blame Sophie for the accident, and instead pointing his finger at police.
He called for sweeping reforms to the way police motorcades are run, and in a visit to the scene of the accident today he blamed motorbike outriders who "endanger the public" when they drive ahead to clear traffic.
On May 24, a Buckingham Palace spokesperson said: "The Duchess of Edinburgh is deeply saddened to hear that Helen Holland has passed away.
"Her Royal Highness's deepest condolences and sympathies go to all of Ms Holland's family."
It is understood Sophie planned to get in touch privately with Ms Holland's family.
The IOPC has been investigating the incident and has taken CCTV from nearby properties for examination.
Retired antiques dealer Martin Hennessy, 62, previously told the Mirror how he saw police cars swarming the scene following the collision.
He said: "When you get to the junction you have to step out to see if anything is coming, that’s when she was hit.
"I came out to walk the dogs and that when I saw this thoroughfare. She’d been thrown across the road and the ambulance were treating her."
Police said at the time there had been no other injuries and enquiries into the crash were ongoing.
