The Queen has said she is "enormously proud" of Prince Charles' achievement in setting up the Prince's Trust.
She paid the tribute during a visit along with the Duke of Edinburgh at the trust's headquarters in central London.
The Queen said there was "no greater pleasure" than knowing the "principles of public service and duty to others" were entrusted into his care.
The prince, who is 60 on Friday, set up the charity 30 years ago with pay he received on leaving the Royal Navy.
In a short speech at the headquarters, near Regents Park, the Queen said: "As the Prince of Wales, our son, approaches his own 60th birthday, may I say that we are both enormously proud to have been reminded here today of his personal contribution to this remarkable organisation.
Vision and conviction
"For Prince Philip and me there can be no greater pleasure or comfort than to know that into his care are safely entrusted the guiding principles of public service and duty to others."
The Queen said the trust, supported by the prince's "vision and conviction", had transformed "countless lives".
The Queen and Prince Philip met with volunteer staff and young people who had been helped by the charity.
Ricky McCalla explained how, after his dancing career had been cut short when he was shot in the neck during a car-jacking, he decided to divert young people from crime by encouraging them to create music.
Fund-raising performance
With the help of the Prince's Trust he set up Frosted Ice Inc and the Ice Box studio in Crystal Palace.
A fund-raising gala performance in aid of the trust will take place later.
The Prince of Wales launched the charity in 1976 with �7,600 severance pay from the Navy.
He had been inspired by concern about the fact too many young people were being excluded from society through lack of opportunity.
The organisation started with 21 pilot projects, and grants were given to a 19-year-old woman to run a social centre for the Haggerston housing estate in east London and to two ex-offenders to run a fishing club.
The charity now has an annual turnover of more than �50m, almost 8,000 volunteers and staff, and has helped more than half a million young people.
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