Police are investigating after a package claiming to contain deadly anthrax was sent to St James' Palace addressed to Meghan Markle, who is due to marry Prince Harry in just over three months.
Tests confirmed that the package contained harmless white powder – but the Metropolitan Police considers the threat so serious it is launching a full investigation to establish the identity of the sender and whether it is linked to another package sent to the Houses of Parliament the following day.
Police are also investigating an allegation of malicious communications, contrary to the Communications Act, relating to the same package.
The incident is being investigated by the Met's Counter Terrorism Command as a racist hate crime. No arrests have been made.
The London Evening Standard reported on Thursday morning that the incident, on 12 February, caused a full security alert at the palace and that the package was intercepted before it could reach the couple.
Scotland Yard said in a statement: "Police are investigating after a package containing a substance was delivered to St James's Palace on Monday, 12 February.
"The substance was tested and confirmed as non-suspicious.
"Officers are also investigating an allegation of malicious communications which relates to the same package, and it is being treated as a racist hate crime.
"The matter is being investigated by officers from the Met's Counter Terrorism Command."
On 13 February, the Met announced that a parcel containing a similar supposed noxious substance – which also proved to be harmless – was sent to the Houses of Parliament.
The Met said that the two incidents are not believed to be connected.
There have been no arrests related to either package.
Prince Harry is due to marry Markle on Saturday 19 May in Windsor.