Zara Tindall has paid an emotional tribute to her world championship-winning horse Toytown, who has had to be put down.

The Queen’s granddaughter said she was “heartbroken” to tell the world “the most incredible athlete with the biggest heart”, who had been retired from competing, died on Tuesday morning.

She rode the chestnut gelding to an individual three-day eventing gold medal at the World Equestrian Games in Germany in 2006, which followed the pair winning individual and team European eventing titles in 2005.

They won another European team gold in 2007.

Zara said in a statement: “I’m heartbroken to say that yesterday morning I had to say goodbye to my greatest friend and horse of a lifetime, Toytown. He was the most incredible athlete with the biggest heart, European and World champion back to back.

“He made my career and I couldn’t be more grateful to him for the amazing times we had together. He was a huge part of my family, an amazing animal and a true champion. I will miss you forever.”

A spokeswoman for Mrs Tindall said Toytown, thought to be 25 years old, was put down for medical reasons.