A and B Batteries were authorized on 20 October 1871. For the last year the Regiment of Artillery has been celebrating its 150th birthday (because in true Canadian Army fashion we ignore the fact that numerous Militia batteries predate A and B Batteries by many decades).
From October 4th to October 22nd of last year, 1 RCHA and the RCA Band formed the Queen's Guard at Buckingham Palace and Windsor Palace.
Allowing the Queen to connect with many members of the Regiment:
I have no idea where the actual idea for the title came from but my guess is that there have been discussions back and forth over the last year that led to this honour.