Kate Middleton is pictured leaving Windsor Castle in car with William as she heads for 'private appointment' - while Prince makes his way to Commonwealth Service at Westminster Abbey

The Princess of Wales has been pictured alongside Prince William leaving Windsor Castle today - just hours after she apologised for digitally editing a family photo released on Mother's Day.

The Prince of Wales was heading to Westminster Abbey for the annual Commonwealth Day service this afternoon with his wife beside him. 

But rather than an extraordinary return to royal duties, MailOnline understands that Kate was heading to a private appointment instead.

It is not known where the Princess of Wales was going, but it was clearly on her husband's route into central London because he arrived alone for the 2.45pm service attended by senior royals including Queen Camilla and Princess Anne.

Kate had looked out of her window as William appeared to read some notes on his phone as they were swept out of the grounds of Windsor Castle in a blue Range Rover that later dropped William at the Abbey without her.

The mother-of-three was not expected to be seen in public until after Easter following abdominal surgery and two weeks in a private London hospital in January.

It came as Kensington Palace came under increasing pressure to release the original Mother's Day photograph after the Princess of Wales apologised after she admitted had edited the family portrait of herself sitting with Prince George, Princess Charlotte and Prince Louis.