The monarch, 95, who already had the official engagement set in her diary, met the incoming Defence Services Secretary Major General Eldon Millar, and his predecessor Rear Admiral James Macleod at Windsor Castle on Wednesday.
WATCH: The Queen seen for the first time since COVID-19 scare
On Tuesday, the Queen was also pictured as she held virtual audiences from her Berkshire abode.
The Queen also held virtual audiences on Tuesday
It emerged last week that Charles had recently met with his mother, but a palace source said at the time that the Queen was not displaying any symptoms.
The source said the situation would continue to be monitored, but a running commentary would not be provided on the monarch's health.
Prince Andrew will no longer face a jury trial
On Tuesday, Prince Andrew, 61, agreed an undisclosed out-of-court settlement with Virginia Giuffre, after she sued him claiming she was trafficked by paedophile Jeffrey Epstein to have sex with the royal when she was 17 and a minor under US law.
The Duke was stripped of his military affiliations and royal patronages last month, and will no longer use the style 'His Royal Highness' in any official capacity.
Make sure you never miss a ROYAL story! Sign up to our newsletter to get all of our celebrity and royal news delivered directly to your inbox.