Princess Anne, who is widely known as the hardest working royal, appears to also be a stickler for the rules because, the royal just refused to break protocol even with Queen Camilla 's permission. On Wednesday, Camilla was presented an honorary doctorate of literature by her sister-in-law Princess Anne.

The two women took part in a rare joint engagement at the University of London, where the Princess Royal presented her sister-in-law with an honorary doctorate

Princess Anne and Queen Camilla made a rare public appearance together earlier this month, with one expert claiming the Princess Royal showed her true feelings

Queen Camilla returned to royal duties for the first time since Buckingham Palace announced she had been diagnosed with a chest infection which affected her timetable

Camilla, 77, and Anne have grown close since Her Majesty joined the royal family in 2005 following her wedding to King Charles.

Queen Camilla's effort to show deference to her sister-in-law Princess Anne during a rare joint royal engagement was graciously declined, as the two navigated longstanding royal protocol at the University of London's Foundation Day on Wednesday.

Queen Camilla was presented with a special honor by none other than her sister-in-law, Princess Anne. Camilla, 77, was awarded an honorary doctorate of literature by The University of London on Wednesday0.