The Duke of Cambridge said his spaniel Lupo was "coping alright" with the new addition to the family.
Prince William said, "As a lot of people know who have got dogs and are bringing a newborn back, they take a bit of time to adapt, but he's been alright so far."
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Michael Fallon has received reassurances from his US counterpart that security ties with Britain will "endure" following a vote for Brexit.
On Friday, police said it appeared the girl had shot herself in the face with the weapon.
The showers will be slow-moving, heavy and thundery at times, particularly in central and eastern areas.