Britain, Hanover, & Brunswick-Luneberg

Would someone clarify for me the relationship among the reigning houses
of these three states during the period when the crowns of Britain and
Hanover were unified? Who was George III's regent in Hanover and what
was their relationship to the Duke of Brunswick who appears to have
been (1) George III or (2) somebody else who reigned in Brunswick which
appears to be (1) one-and-the same with Hanover or (2) someplace else.
I have tried very hard to figure this out by searching alt.talk.royalty
and elsewhere with - as must be obvious - no success. Thanks.

Don Aitken...

linked from there will give you a start. The dukedom of Brunswick
(Braunschweig) was established in the 13th century, and embarked on a
long career of division, subdivision and merger, reflecting the
reproduction and mortality of the Welf family. *All* of the rulers of
any of these states were dukes of Brunswick, whether in Brunswick,
Grubenhagen, Gottingen, Luneburg, Wolfenbuttel or wherever (most of
them were dukes of Luneburg as well).

In the 17th century most of these fragments were brought together into
the Electorate of Hanover (Hannover in German); the Electors continued
to be dukes of Brunswick, in addition to their other titles. There
were a few small fragments not included in this merger, which came
together in the 18th century under the duke of Brunswick-Wolfenbuttel,
who celebrated by using the title of simply Duke of Brunswick
(although the Electors, later Kings, of Hanover also continued to use
that title). This line became extinct in 1884; the Hanoverian line,
succeeded to its territories (having lost their own in 1866) after
complications too tedious to go into. Those territories included the
*town* of Brunswick. The last common ancestor of these two lines was
Ernst I of Brunswick, who died in 1546.

As to George III, he was represented in Hanover by a member of his
family; during the later part of the reign, this was his seventh son,
the Duke of Cambridge.

Uwe...

To add some confusion, George IV (of the UK & Hannover) was also the
uncle of the last two dukes of Brunswick and their legal guardian and
regent for Karl III. (of Brunswick) in the time of the minority (1815 -
1823). The ducal powers were apparently delegated at that time to a
privy council of three noble members (see:
34+35 on pages 10+11).