When Darren Beadman looks back on his glittering career in the saddle, Octagonal stands tall as a true champion.

Beadman rode Octagonal to five of his 10 Group One wins and said he was shocked and saddened to hear the horse had been euthanised on Saturday morning at the age of 24..

Four of their Group One wins together came in the autumn of 1996 when Octagonal claimed the Canterbury Guineas, Rosehill Guineas, Mercedes Classic and Australian Derby, racing four Saturdays out of five.

He was up against what is still hailed as a benchmark group of three-year-olds including Saintly, Nothin' Leica Dane and Filante.

"He was a back marker so he was always vulnerable and never won by big margins," Beadman said.

"So he was always vulnerable but he went to war for you."

Beadman said their four-win sequence in the autumn of 1996 by bare margins showed Octagonal's true standing.

"Sometimes you'd have your heart in your mouth but I always had faith in him and he delivered," Beadman said.

"He was a champion."

In the breeding barn, Octagonal sired his own champion Lonhro who in turn produced one of his own, Pierrro.

Octagonal was raced by Jack and Bob Ingham and was part of the package when the latter sold his Woodlands racing and breeding operation to Sheikh Mohamamed.

"The Big O as he was affectionately known, was still bright and alert mentally but was struggling physically," Darley said on Saturday.

From the first crop by Cambridge Stud stallion Zabeel, Octagonal was prepared throughout his career by the Ingham's private trainer John Hawkes.

"It is a sad day as Octagonal is an old favourite of everyone and he will be sorely missed. He was such a lovely horse to deal with and such a big part of Woodlands," John Sunderland, Woodlands general manager said.

Octagonal will be buried at Woodlands, where he has spent the majority of the past 16 years, alongside Canny Lad.