ZARA Tindall and Peter Phillips are known for being the grandchildren of the late Queen Elizabeth and Duke of Edinburgh.
Their father Captain Mark Phillips has another daughter called Felicity who has flown under the radar - here is all you need to know about her.
Who is Zara Tindall's half sister Felicity Tonkin?
Felicity Tonkin is the daughter of Captain Mark Phillips and former art teacher Heather Tonkin.
Felicity is the result of an affair between the pair and is only four years younger than her royal half-sister Zara.
Reportedly, like her older sister, Felicity is a keen equestrian who works as a specialist vet after studying at Massey University.
As a student, Felicity posed nude for the university's prolific Barely There calendar which sees vet students strip and pose nude for charity.
She's married to accomplished polo player Tristan Wade who has played in front of the late Queen Elizabeth and Duke of Edinburgh at Windsor.
It's believed the couple and their son James live in a £1.5million property in Auckland, New Zealand, where they keep their horses.
Who is Felicity Tonkin's mother Heather?
Heather and Mark are believed to have met at a riding clinic in Auckland while Mark was still married to Princess Anne.
It's alleged the pair had a one-night stand at a nearby hotel where Mark infamously left his riding boots outside the door so she could find the right room.
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Heather later found out she was pregnant with Felicity but a shocked Mark tried to convince her to have an abortion.
Instead she kept her unborn baby and went through with her pregnancy, nicknaming her little girl "Bunny".
Has Felicity Tonkin ever met her father and does she have contact with the Royal Family?
Mark Phillips, according to royal sources, has been in denial about his daughter since the day she was born.
A close friend told New Idea "he just never accepted it and he couldn't cope with it".
Despite refusing to have contact with his daughter, Mark secretly paid Heather $12,000 (£5,790) a year in child support.
However, his payments trailed off which led to Heather seeking a better deal for her daughter, despite her father refusing to be listed on her birth certificate.
In 1991, a court ordered DNA test proved Mark was Felicity's father.
Heather defended her decision to make the situation public and threaten Mark with court action stating: “I am doing what I am doing for my child.
"I hope and pray Mark will do the right thing and make a proper and legally binding settlement on her.
"I wish I could wake up one morning in the knowledge that the record had been put straight and I don’t have to worry any more.
“Nothing can compensate for the tears I have cried while trying to plan for Bunny’s future, when at any moment I could find myself penniless.
"Bunny throws her arms around me to comfort me, asking why I am sad. But I have never been able to tell her.
"My ambition is to get Mark's public acceptance of her and to be able to enter his name on her birth certificate."
Unfortunately, her father's rejection has left Felicity heartbroken who learned the truth about him when she was eight.
During her time at school, she had to complete a school family tree project which led her to trying to learn as much as possible about her family.
The Daily Express reported she kept a book about Mark by her bed, devouring articles about her British family.
New Idea reported Heather's ex-boyfriend Jason Fowell stated: “She’d have liked a card or something, some sort of recognition.
“She wished she had a father to go to school interviews, that sort of thing.
"I saw her cry about it.”
However, a palace source stated "the story heaped shame on the royal family".
Despite having a younger half-sister, Zara and her brother Peter have had no contact with Felicity.
The palace source revealed: “They just don’t want to get involved and that’s probably the way it will stay.”
In 1999, Mark was asked if he planned to visit his daughter while they both attended the same equestrian event in New Zealand.
He simply replied, “wrong subject”.
Despite being separated at the time the bombshell scandal was revealed, it prompted Princess Anne to begin divorce proceedings which were finalised in 1992.
Mark later married dressage rider Sandy Pflueger in 1997 and the couple had daughter Stephanie.
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They later divorced after it was reported Mark had left her for Lauren Hough, who was 32 years his junior.
In 2022, Mark was spotted at Burghley Horse Trials with rumoured new girlfriend Florence Standaert.
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