She's heiress to one of the richest men on Earth and her mother was a renowned beauty. She could have had her pick of most of the world's princes and to say she was eligible is a bit of an understatement. Yet Princess Zahr, daughter of the Aga Khan, has baffled society-watchers by choosing to marry a down-to earth, ordinary sort of chap--and he's British.

The only daughter and eldest child of the spiritual leader of Ismaili Moslems announced her engagement to 35 year old management consultant Mark Boyden yesterday. She told her parents at the weekend and both the Aga Khan, whose fortune is estimated at 2 billion pounds, and his British-born ex-wife Sally Croker-Poole are said to be wholeheartedly in favour.

Sally, a 57 year old former model and debutante, has all but disappeared from European society circles since the divorce in 1995. She has since remarried French lawyer Phillippe Lizop, who helped to secure her 50 million pounds divorce settlement. "She is my only daughter and I am absolutely thrilled for her," she said at her mansion in Geneva. He's a really nice man and I am so happy for her. They have known each other a while and I think This has been on the cards for some time. I couldn't be more pleased for her."

Zahra, 26, graduated from Harvard University in America in 1994 after studying Third World development.But while her illustrious background could fill volumes, much less is known about her London-born husband-to-be. He is, however, said to be very handsome, well-educated, and from a middle-class farming family in Wiltshire. Mr. Boyden was educated at Oxford, but not exactly amid the dreaming spires. He graduated in business administration and ethics from the poly -- now Brookes University -- where he was remembered by one gushing female staff member yesterday as "really lovely, extremely good looking and charming." He is also believed to be a member of the Institute of Management Consultants. Like his future wife, he is involved in working with his family, dealing with their farming interests.

The Aga Khan's office said the couple, who met on a holiday in France two years ago, plan to marry early next summer. They will divide their time between Britain and France, keeping homes in both countries. Gerard Wilkinson, the Prince's spokesman, said neither he nor his daughter were available for comment. But he added: "The Aga Khan is very proud and happy with their decision to marry. The couple have a lot in common through their work and are both interested in humanitarian issues in Africa and Asia. She is concerned with women's issues in the Third World and he is particularly interested in child labour. The Princess intends to carry on working after she is married.

Friends in Paris said Zahra is no jet-setter, and her work leaves little time for night clubs and parties. She keeps in close touch with friends from her school days in Switzerland and from her spell at Harvard. "Zahra takes after her dad and she is particularly close to her younger brothers Rahmin and Hussein" said a family friend. "She will make a great wife. Her future husband loves the country life and so does she. But until they have children of their own, Mark will have to accept that she continues to give priority to her work."