Meet the secret stepdaughter of Princess Anne who remains a mystery to Zara and Peter

Princess Anne has been busy this week meeting with Gurkha personnel and their families during a visit to Imjin Barracks in Gloucestershire. The 73 year old Princess Royal, who is King Charles' younger sister, is a well-loved Royal figure and is often hailed as the most industrious member of The Firm.

She is wedded to ex-Royal Navy officer Sir Tim Laurence, whom she married in 1992. However, her two offspring - Peter Phillips, 46, and Zara Tindall, 43 - are from her first marriage to Mark Phillips, 75, an Olympic gold medal-winning equestrian.

Anne and Phillips tied the knot in 1973 after meeting five years prior. They parted ways in 1989 due to ongoing relationship issues.

READ MORE: Zara Tindall's 'secret' half-sister Stephanie Phillips announces engagement

Despite not initially wanting a divorce, things took a dramatic turn in 1991 when it was revealed that Phillips had fathered a child with a New Zealand art teacher.

Felicity Tonkin was born in 1985 to Heather Tonkin, who had a brief encounter with Phillips in 1984. Her identity remained concealed for six years, but when the truth surfaced, it sparked one of the biggest Royal scandals ever, reports the Scottish Daily Express.

The pair initially met at an Auckland riding clinic and became friends. The affair occurred when he returned a year later, with rumours suggesting he famously left his riding boots outside his hotel room so Tonkin could locate him.

Reports indicate that Phillips initially proposed an abortion and then proceeded to make monthly payments for the child's upkeep. However, in 1991, Tonkin went public and DNA tests confirmed Felicity as the daughter of Anne's husband.

The latest reports suggest that Felicity has never met her step-siblings Zara and Peter. It is said that they have a good relationship with Stephanie Phillips, their half-sister from their father's second marriage to Sandy Pflueger.

Despite maintaining a low profile, Stephanie requested Peter and Zara's children to be flower girls at her wedding and even extended an invitation to Anne for the big day.