The Prince of Wales and his long term companion Camilla Parker Bowles attended a semi-official engagement together on Tuesday evening.
It was the first time they stepped out together in public at such a formal event.
But their symbolic gesture was marred by a vocal anti-monarchist protest.
Prince Charles and his companion on Tuesday hosted a private gala dinner in honour of the Prince's foundations in the United Kingdom and the United States.
They arrived at the headquarters of the Prince's Foundation in a newly-restored warehouse in Shoreditch, east London, in the same car.
In front of around 100 photographers, they walked the short distance down a red carpet into the building.
Camilla Parker Bowles, who smiled broadly, was wearing a pale pink embroidered full-length evening gown, believed to be by Versace.
The couple did not pose for photographers, despite pleas from the media.
At the same time, they turned a blind eye to a small but noisy group of anti-monarchy protesters who shouted and waved banners.
The demonstrators waved posters saying "Queen Mum Hurry Up and Die" - a reference to the Queen Mother, Charles' grandmother, who marks her 100th birthday this year.
Tuesday's event came just a couple of weeks after the Queen met Parker Bowles for the first time in years at a lunch for the former Greek monarch, King Constantine.
At that time, it was said she would not accompany the Prince on official engagements.
But the Shoreditch dinner was partly a private "thank you" for those who have supported both foundations.
The Prince of Wales Foundation in the U-S supports a variety of charitable issues which are close to the Prince's heart.
The Prince's Foundation in the U-K was set up a year ago as an umbrella group for all the architectural and environmental causes he sponsors.
Guests at Tuesday's event included fashion designers Donatella Versace and Valentino.
Model Elle Macpherson was also on the guest list along with actress Lauren Bacall and Sir Richard and Lady Branson.
The presence of Parker Bowles was another landmark in an increasingly successful campaign by Charles and his advisers to gain public acceptability for the woman who was blamed by Charles' ex-wife, the late Princess Diana, for the breakup of their marriage.