Rex is the Queen's favourite corgi and lives a life of luxury with three other corgi companions in Buckingham Palace. On a visit made by President Donald Trump with his wife Melania Trump and their own dog Mitzi, the Queen suggests that perhaps one of her own corgis might prove to be a suitable mate for Mitzi, who chooses Rex, who is not pleased at all at the prospect of becoming mates with Mitzi.

After Rex evades her multiple times, Mitzi eventually chases him into the dining hall where he accidentally bites the president, deeply angering the Queen.