The Sunday Times of London said the letter -- which the British government suppressed during the 1950s -- was written in 1880. It addressed Princess Frederica of Hanover's decision to elope to Britain with a commoner.
In the letter to Frederica's brother, Victoria expressed her consent to the marriage and informed the German royal family that she had taken in the wayward couple.
"I know well that you, as well as your dear mother ... would have desired another marriage more in accordance with her rank, for Lily is worthy of the highest positions; but she cannot marry without her heart and her heart belongs to another," Victoria wrote.
The kindhearted words about the marriage -- which was opposed by the princess' father -- are at odds with Victoria's public image.
The Times said the letter had been kept secret due to its role in a 1955 legal action.
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