The Duke of Cambridge waas also ful of praise for the portrait.
Prince William said:: "It's beautiful, it's absolutely beautiful."
The Cambridges later attended a private breakfast reception at the London gallery to mark the unveiling.
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Becoming clear and frosty overnight. Bright and dry on Monday.
An Essex councillor is appealing for help to find out what happened to her "beautiful, much-adored" daughter after she was found dead.
Frost and freezing fog overnight but milder with some rain tomorrow.