Buckingham Palace says Peter Phillips and his wife, Autumn, are expecting their second child, who will be Queen Elizabeth II's second great-grandchild.
The baby is due in March.
Queen Elizabeth II becomes great-grandmother
The palace said Friday that the Queen, her husband the Duke of Edinburgh and Autumn's family are delighted by the news.
The couple already have a daughter Savannah — born in December — who is 12th in line to the throne and was the queen's first great-grandchild.
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Peter Phillips, the son of Princess Anne, is the queen's oldest grandchild. He is 11th in line to the throne, and married Montreal-born Autumn in May 2008 at Windsor Castle.