Outstanding New Zealand mare Princess Coup has been retired due to ongoing tendon problems.

Trainer Mark Walker noticed filling in her tendon when she returned to his stable after coming out of quarantine following her Australian spring campaign.

Princess Coup was dominant in the 2007 New Zealand Oaks and went on to the country's richest race, the $2 million Kelt Capital Stakes, later that year and again in 2008.

Her biggest win in Australia came in last year's Group Two St George Stakes.

Although she failed to register a Group One victory in Australia, Princess Coup was placed five times including when third in the 2007 Caulfield Cup and second in the 2008 Australian Cup.

Co-owner Ray Coupland said Princess Coup's breeding future had yet to be decided and he could not say whether she would remain under her current ownership interests, or whether a sale could be on the agenda.

Coupland was able to reflect on the mare's career which began when she was bought for $A260,000 at the 2005 Magic Millions Sale at the Gold Coast by trainer Mark Walker and Te Akau Stable manager David Ellis.

"The second Kelt Capital was probably the highlight because of a number of reasons," Coupland told The Press newspaper.

"I had not been there the previous years and had been through a tough time with health issues leading into this year and there was a lot of emotion involved.

"Years ago in Timaru, when I started out with horses, I used to say one day I was going to race a really top horse. I suppose it was a pipe dream then, but it happened. She has given us so many thrills."

Walker said Princess Coup has been "just such a pleasure, a real sweetie to train".

She retires with 12 wins from 33 starts including four at Group One level.