However the couple's marriage wasn't a happy one, and Princess Anne started an affair with the Queen’s equerry Timothy Laurence.
Then, in April 1989, love letters from Timothy were taken from her personal briefcase and leaked to The Sun newspaper.
The newspaper handed over the letters to police who launched an investigation into the crime.
After an extensive investigation, however, the thief who stole the letters was never found.
When questioned over the investigation, Detective Chief Superintendent Roy Ramm told the 2002 Channel 4 documentary The Real Princess Anne that the inquiry was “unusual”.
He said: “You’re dealing with a theft in a royal palace and the victim happens to be a princess.
“You then find that what’s been stolen are letters from her lover.
“You then have to deal with that by interviewing loads of people in palaces in the full glare of the world’s media and this very soon became the most talked about story.”
He added: “Frankly, we came up against a dead end and we went to the princess and said: ‘Look we’re very sorry, we cannot tell you definitively who stole your letters‘.”
Princess Anne eventually came clean about the affair, and Buckingham Palace released a statement on the matter.
A statement read: “The stolen letters were addressed to the Princess Royal by Commander Timothy Laurence, the Queen’s Equerry.
“We have nothing to say about the contents of personal letters sent to Her Royal Highness by a friend which were stolen and which are the subject of a police investigation.”
Princess Anne, 69, and Mark promptly separated and then divorced in 1992.
Her relationship with Timothy, 65, was then out in the open, and the couple were wed in 1992. They remain married to this day.