Interpretation

Queen Victoria, alone on the throne
After the demise of Albert who was her only husband
and the first to share the royal bed,
Will remain seven years in mourning,
And she will have a long and tumultuous reign.

History After the death of her husband Albert, Queen Victoria never remarried and she reigned alone on the throne until her death in 1901:
In 1837 Queen Victoria took the throne after the death of her uncle William IV. Due to her secluded childhood, she displayed a personality marked by strong prejudices and a willful stubbornness. On Feb 10th, 1840, only three years after taking the throne, Victoria took her first vow Premier au and married her cousin, Prince Albert of Saxe-Coburg-Gotha. Their relationship was one of great love and admiration. Together they bore nine children - four sons and five daughters: Victoria, Bertie, Alice, Alfred, Helena, Louise, Arthur, Leopold, and Beatrice.
(http://www.victorianstation.com/queen.html)

Prince Albert died of typhoid fever in December 1861.(D'unique éteint, premier au lit d'honneur) Victoria continued to carry out her constitutional duties (la dame seule au règne demeurée) such as reading all diplomatic despatches. However, she completely withdrew from public view and now spent most of her time in the Scottish Highlands at her home at Balmoral Castle. Victoria even refused requests from her government to open Parliament in person. Politicians began to question whether Victoria was earning the money that the State paid her. While at Balmoral Queen Victoria became very close to John Brown, a Scottish servant. Victoria's friendship with Brown caused some concern and rumours began to circulate that the two had secretly married. (In any case Nostradamus says Premier au lit d'honneur, which means there was a second which could very well have been John Brown). Hostility towards Victoria increased and some Radical MPs even spoke in favour of abolishing the British monarchy and replacing it with a republic...
(http://www.spartacus.schoolnet.co.uk/PRvictoria.htm)

Thus the sept ans de douleur éplorée, seven years in mourning could mean that Albert having died in 1861, and Victoria being in constant contact with her confidant John Brown, it only seems natural that, after seven years of mourning, she finally fell for the faithful servant. At least, this is what Nostradamus saw in the vision.

Even though she is remembered as the greatest queen of England, Victoria was not always a popular queen:
Soon afterwards an attempt was made to kill Victoria while she was driving in her carriage in London. Further assassination attempts took place in 1842 (twice), 1849, 1850, 1872 and 1882.(Puis longue vie au règne par grand heur)
(http://www.spartacus.schoolnet.co.uk/PRvictoria.htm)
Her relationship with the House of Commons was at times tumultuous, to say the least:
Queen Victoria was very upset when Gladstone replaced Disraeli as premier in 1880. When Disraeli died the following year, Victoria wrote to his private secretary that she was devastated by the news and could not stop crying. (Puis longue vie au regne par grand heur) Gladstone's relationship with Victoria failed to improve. As well as her objection to the 1884 Reform Act, Victoria disagreed with Gladstone's foreign policy. William Gladstone believed that Britain should never support a cause that was morally wrong. Victoria took the view that not to pursue Britain's best interest was not only misguided, but close to treachery.
(http://www.spartacus.schoolnet.co.uk/PRvictoria.htm)