Phillips is "close friends" with former glamour model Katie Price.

Katie - who is also known as Jordan - claims she got to know the 27-year-old granddaughter of Queen Elizabeth at the Burghley Horse Trials in Lincolnshire, England, last month.

Katie's agent confirmed: "They are very friendly but not many people know that.

"Katie never talks about her friendships with other celebrities and she won't discuss her friendship with Zara, but yes, there is a friendship. She is going to Gatcombe Park with Zara and can't wait."

The 30-year-old model was invited to the three-day horse riding event at Gatcombe Park, Gloucestershire, by Zara's mother Princess Anne, who organises the event.

Katie is horse enthusiast who is keen to be taken more seriously in the world of dressage - she even performed a routine at last year's Horse Of The Year Show.

A source told Britain's The Daily Mail newspaper: "Katie said they talked lots about horses. Zara thought Katie would love her mother's horse show at Gatcombe Park and invited her to come along.

"They stay in touch via text and email mostly. They are two women from two very different worlds but they share a passion for horses and riding."

Katie recently revealed she was excited about attending the eventing festival, especially as it would give her 21-month-old daughter Princess Tiaamii the chance to meet royalty.

She said: "Even Princess Anne knows how much I love horses and has invited me to her house to watch polo. I'll definitely go for lunch with her, so my Princess can meet a real-life princess."

The model also revealed it was not the only invitation from the royal family she had received recently.

She said: "We were invited to lunch at Buckingham Palace but we couldn't go because we were in America. I was gutted."