Which regent could on February 6 2012 celebrate the 60th year and hereby diamond jubilee on the throne?

Explanation

February 6 2012 was a day of celebration in the countries of the Commonwealth. It was the Diamond Jubilee of Queen Elizabeth II which marks the 60th anniversary of her accession to the thrones of the United Kingdom, Canada, Australia and New Zealand, and the 60th anniversary of her becoming Head of the Commonwealth. Apart from Queen Elizabeth II it is only Queen Victoria who has celebrated a diamond jubilee on the british throne.