This was an anthology of children’s stories or children’s literature that was in print in the middle 1970’s. The hard cover was a robin’s egg blue and the book was relatively thick, but *not* coffee table sized. One of the stories was about a Spanish infanta (princess) who was under the protection of her duenna (like a guardian or nanny). Possibly also had Hans Christian Andersen fairy tales but not sure.
Lost Classics of Teen Lit: Name That Book! 
Could this be one of Andrew Lang’s collections? Either one of the Fairy Books, or more likely, his “Book of Princes and Princesses.” A Google image search shows that it had a blue cover, something that is likely to remain consistent given how linked the titles are with their cover colors.
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Mention of the Infanta made me think it might have included Oscar Wilde’s story “The Birthday of the Infanta,” and it looks like there’s a 1978 anthology of his fairy tales with that title and a robin’s-egg blue cover! Is this it? https://www.goodreads.com/en/book/show/704035
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