Buckingham Palace to display never-before-seen portraits of Prince William and Prince Harry

The royal family is celebrating Prince Charles' 70th birthday all year long -- and one of this summer's exhibitions will give a never-before-seen look at some of the royals' prized portraits.

On Monday, the Royal Collection Trust announced details of the "Prince and Patron" collection, which will go on display at Buckingham Palace this summer. The exhibition will feature over 100 works personally selected by His Royal Highness, the Prince of Wales, and include several portraits of royal family members that have never been seen by the public.

The collection includes two oil sketches of Charles' sons, Prince William and Prince Harry, which were done by artist Nicky Philipps in preparation for her painting of the royal brothers, their first official double portrait, which first went on display in 2010. The sketches now hang on the walls of Highgrove, the private residence of Prince Charles and his wife, Camilla, Duchess of Cornwall.

Artist Nicky Philipps stands with her work, 'Prince William and Prince Harry: a new portrait by Nicky Philipps' at the National Portrait gallery in central London, on January 6, 2010.

Artist Nicky Philipps stands with her work, 'Prince William and Prince Harry: a new portrait by Nicky Philipps' at the National Portrait Gallery in London.

LEON NEAL/AFP/Getty Images

Also on display will be an oil sketch of Charles' grandmother, Queen Elizabeth The Queen Mother, which was produced by artist Michael Noakes as a study for a group portrait marking the 25th wedding anniversary of the Prince of Wales' parents, Queen Elizabeth II and Prince Philip, the Duke of Edinburgh.

"I acquired it from the artist as I felt it brilliantly captured her likeness, and, above all, reminds me of the essence of my grandmother's personality," Charles explained in a video about the piece on the Royal Collection Trust's Twitter page. "I admire it often when in residence at Clarence House."

Celebrations for Charles' 70th birthday have been underway all year, and in fact, Prince Harry and Meghan Markle's first public engagement following their spectacular royal wedding in May was at a garden party celebrating the prince's upcoming milestone. Harry spoke at the event, which also served to honor first responders on the anniversary of the tragic Manchester bombing.

"His enthusiasm and energy are truly infectious; it has certainly inspired William and I to get involved in issues we care passionately about and to do whatever we can to make a difference," Harry told the crowd of his father's life and legacy. "In fact, many of the issues William and I now work on are subjects we were introduced to by our father growing up. His passion and dedication are remarkable, and seeing so many of you here today, I cannot fail but to be in awe of the drive he has had for so many years, to contribute to the enrichment of society both in this country and around the world."

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