From The Times Online:

An image of Elizabeth I as a teenager — one of two painted during her lifetime — has emerged from beneath centuries of incompetent touching up by later artists.
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Although the portrait was known to portray Elizabeth, it was thought to be an insignificant copy from the 18th or 19th century.
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The importance of the painting, which will be on sale at the Grosvenor House Art & Antiques Fair this week for £800,000, was discovered by Philip Mould, an art dealer and specialist in historical portraits.

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And from The Telegraph (with image)

A rare portrait depicting Elizabeth I as a vulnerable teenager rather than a powerful queen has been rediscovered by an expert more than 450 years after it was painted.
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The picture by an unknown artist is only the second known portrait of Elizabeth as a young princess - the other is in the Royal Collection - and projects a softer image very different from the later paintings showing her as a strong monarch.

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Here is a link to the original portrait that this one is copied from.