Pictures showed the smiling 95-year-old monarch holding an audience with the new ambassadors for Latvia and Ivory Coast.
The queen carried out the engagements from her Windsor Castle home to the west of London where Philip's funeral was held two weeks ago, and it was the first since a period of official royal mourning ended.
We are here today in St George's Chapel to commit into the hands of God the soul of his servant Prince Philip, Duke of Edinburgh. With grateful hearts, we remember the many ways in which his long life has been a blessing to us.
"We therefore pray that God will give us grace to follow his example, and that, with our brother Philip, at the last, we shall know the joys of life eternal."
"The death of Prince Philip fills me with great sorrow," she said in a statement posted by her spokeswoman on Twitter. "His friendship to Germany, his straightforwardness and his sense of duty will not be forgotten," she added.
"We remember the Duke ... above all for his steadfast support for Her Majesty the Queen, not just as her consort, by her side, every day of her reign, but as her husband, has strength and stay of more than 70 years. And it is to Her Majesty, and her family, that our nation's thoughts must turn today."
"The United Kingdom has lost an extraordinary public servant in Prince Philip."
"It was with great sadness that a short time ago I received word from Buckingham Palace that His Royal Highness the Duke of Edinburgh has passed away at the age of 99.
"Prince Philip earned the affection of generations here in the United Kingdom, across the Commonwealth and around the world.
Philip, the Duke of Edinburgh, was admitted to the private King Edward VII's Hospital on Feb. 16 after he felt unwell and was given treatment for an unspecified, but not COVID-19-related, illness.
Since being admitted, the duke has been publicly visited only by his eldest son Prince Charles, the heir to the throne.