One of the Queen's senior assistants has reportedly called staff to an "emergency meeting" at Buckingham Palace, and no one knows why.
Staff from as far away as Scotland have been called in, the Daily Mail reports, fuelling speculation a major announcement concerning the Queen or Duke of Edinburgh is forthcoming.
Lord Chamberlain, the most senior officer of the royal household, and the Queen's Private Secretary Sir Christopher Geidt, are set to speak, the paper reports.
One source told the Mail staff meetings aren't uncommon, but this time they've been summoned "at the eleventh hour".
"[It] suggests that there is something major to be disseminated."
Buckingham Palace has refused to comment on the rumours.
The Queen is 91 and her husband turns 96 in June.
The official royal family Twitter account posted photos of the Duke at the Lord's cricket ground in London overnight (NZ time).