Queen Elizabeth II meets Kate Middleton's parents

(CBS) Queen Elizabeth II and Kate Middleton's parents met for the first time on Wednesday, just days before the royal wedding.

The monarch, who turns 85 tomorrow, and her husband, Prince Philip, 89, had lunch with their grandson's future in-laws, Michael and Carole Middleton, at Windsor Castle, Buckingham Palace confirmed.

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The invitation was extended some time ago, according to reports.

A source said the meeting had a "warm atmosphere," People magazine reports. A few members of the queen's royal household were also present.

A Buckingham Palace spokeswoman confirmed the gathering to the U.K.'s Press Association, saying, "The Queen and the Duke of Edinburgh hosted Mr and Mrs Michael Middleton at a private lunch at Windsor Castle today."

Middleton's father, 61, and mother, 56, are self-made millionaires who started a mail-order party supplies business called Party Pieces.