You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Queen_Victoria

Context:
Napoleon III, since the Crimean War Britain's closest ally, visited London in April 1855, and from 17 to 28 August the same year Victoria and Albert returned the visit. Napoleon III met the couple at Dunkirk and accompanied them to Paris. They visited the Exposition Universelle (a successor to Albert's 1851 brainchild the Great Exhibition) and Napoleon I's tomb at Les Invalides (to which his remains had only been returned in 1840), and were guests of honour at a 1,200-guest ball at the Palace of Versailles.

Question:
When were Napoleon I's remains interred in his mausoleum?

1840