The monarch, 95, held virtual audiences at Windsor Castle via video-link on Tuesday.
It is the first time she has been seen undertaking her royal duties since Philip, 99, died peacefully at the Berkshire royal residence on April 9.
The Queen appears on a screen by videolink from Windsor Castle for a virtual audience with Ivita Burmistre, ambassador of Latvia (Yui Mok/PA)
The Queen, no longer in a black mourning outfit, was dressed in a pale blue floral dress which featured large purple, white and yellow flowers, with a three-string pearl necklace and a diamond brooch as accessories.
She was pictured on a computer screen smiling as she held two audiences with the ambassador from the Republic of Latvia, and the ambassador from the Republic of Cote d’Ivoire, who were at Buckingham Palace.