The party is over, but the dream will live on.

Black Caviar, arguably the greatest horse to race in Australia in 80 years and one of the best the world has ever seen, has retired undefeated, unharmed and with her record unblemished.

Her part-owner Neil Werrett and trainer Peter Moody fought back tears as they broke the news at Caulfield on Wednesday.

"Our lovely horse, our wonderful horse, as you can see, has never looked better," Werrett said.

"And today we want to announce she is retiring."

The end of Black Caviar's invincible career came at Randwick last Saturday with her 25th win from as many starts - and one which led to Wednesday's decision.

After considering their options - a race in Brisbane, a return trip to Royal Ascot or one more roll of the dice next spring - the world champion mare's owners and her trainer decided to do what is best for their horse.

"It's the right time to call it a day on what's been a wonderful career of one of the finest horses we have ever seen," Moody said.

"We thought long and hard about racing on for another season. We thought about Royal Ascot, we thought about Brisbane and we thought about Adelaide, but we believe she has done everything we've asked her to do.

"She couldn't have possibly done any more."

For Moody and the mare's nine owners, the end of the "most amazing journey we could have hoped for" was made less traumatic by the knowledge Black Caviar had extended her career beyond what they thought possible.

After she came within a few steps of being beaten at Royal Ascot last June, they all believed she had run her last race.

But a long rest and constant care and attention enabled her to return to the track in February and to add three more wins to a record unequalled in Australian racing.

"We've been fortunate to bring her home here and I think the owners are to be congratulated on allowing me to race her on and give the Australian public three more opportunities to see her," Moody said.

Jockey Luke Nolen, who rode Black Caviar in all but three of her wins, thanked her for making his career.

"Horses like Black Caviar are career defining. I thank her for the memories and now that it's come to an end I can appreciate it," Nolen said on Twitter.

Black Caviar's racing career began in April, 2009 with a five-length win in a two-year-old handicap at Flemington.

She won a Listed race at her next start by six lengths and then had four months off, returning to win again in her first start as a three-year-old.

From there her career took off with her closest brush with defeat coming at her fourth start when her stablemate Wanted got within three-quarters-of-a-length.

For the next three years no horse threatened her as she reeled off victory-after-victory.

Only when she went into the Diamond Jubilee Stakes at the Royal Ascot meeting last June did defeat seem possible when Nolen relaxed 50m from the finish and the French runner Moonlight Cloud almost caught her.

"We decided 25 was a great number and we thought she did us all proud on Saturday," Moody said.

Black Caviar will parade at the Caulfield race meeting on Saturday before letting down over the winter and then going to a yet to be chosen stallion.

Her owners have ruled out a visit to the English champion Frankel, one of the few horses ever to be placed above her on official rankings.