A spokesman for Clarence House, Charles's official London residence, refused to comment on the report, saying they did not discuss the private time of members of the royal family.
But a royal source told AFP that 28-year-old Prince William often spent time with groups of friends at Birkhall when Charles was not there "and this was just one of those occasions."
Middleton's mother Carole appeared in the pictures lying in grass receiving instructions on shooting -- a popular pastime for Britain's royals -- while her husband stood watching.
The Daily Mail said that in the protocol-heavy world of the royal family the visit was "highly symbolic" and would have been approved by Prince Charles and Queen Elizabeth II.
It added that it was the "clearest sign yet that Kate and Prince William are poised to announce their engagement after a marathon eight-year courtship".
Prince William, who is second in line to the throne, met Middleton when they were both students at Saint Andrew's University in Scotland.
He is currently serving as an RAF search and rescue co-pilot.
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But a royal source told AFP that 28-year-old Prince William often spent time with groups of friends at Birkhall when Charles was not there "and this was just one of those occasions."
Middleton's mother Carole appeared in the pictures lying in grass receiving instructions on shooting -- a popular pastime for Britain's royals -- while her husband stood watching.
The Daily Mail said that in the protocol-heavy world of the royal family the visit was "highly symbolic" and would have been approved by Prince Charles and Queen Elizabeth II.
It added that it was the "clearest sign yet that Kate and Prince William are poised to announce their engagement after a marathon eight-year courtship".
Prince William, who is second in line to the throne, met Middleton when they were both students at Saint Andrew's University in Scotland.
He is currently serving as an RAF search and rescue co-pilot.
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