Scotland Yard chief Sir John Stevens says he would be prepared to interview Prince Charles as part of his inquiry into the death of Princess Diana.
Sir John is expected to visit the tunnel where the pair died
He told BBC One's Breakfast with Frost programme he would pursue the evidence wherever it led.
He will be investigating allegations - most prominently by Mohamed Al Fayed - that the princess's death in Paris in 1997 was not an accident.
Sir John said he hoped his inquiry would close the book on the death.
A French investigation into Diana's death in a car crash in the Pont d'Alma tunnel blamed chauffeur Henri Paul, who also died, concluding he had taken drink and drugs and had been driving too fast.
But conspiracy theories about the deaths have persisted, and the coroner conducting her inquest asked Scotland Yard to establish if there was any truth to foul play rumours surrounding the crash.
The crash happened as Diana, her companion Dodi Fayed and bodyguard Trevor Rees-Jones were being driven from the Ritz hotel, followed by photographers. Only Mr Rees-Jones survived the crash.
Ex-police chief John Stalker has said Prince Charles should be quizzed over a letter in which Diana reportedly suggested he was plotting to kill her.
Sir John said: "I want to complete, with my team, that investigation, by the end of the year. We have got a team of eight on that now. We have enhanced it also with an expert on accidents.
"At some stage myself, the coroner and others will be going to Paris to have a look in detail at what is happening there, to get a feel for the route, and get a feel for where the accident took place among other things.
"So there is a two-pronged approach to this. One is to ensure, is there anything else that we can do to assist the French in their inquiries and to assist the coroner in coming to his conclusion.
"The second part of it, which is just as important in my view, is that the allegations that have been made have to be investigated, and proved one way or another."
Asked whether that meant that he would have to interview Charles, Sir John said: "That will depend on where the evidence takes us. If the evidence suggests that we have got to interview whoever, we will do that, we have to do that to ensure that the job is done thoroughly, and I think everybody understands that."