Last year's Irish Oaks winner and Prix de l'Arc de Triomphe runner-up Sea Of Class has died after losing a battle with colic.
It had been announced a fortnight ago that the filly would not race again but hopes were still that she would recover and have a career at stud.
Sea Of Class with James Doyle after winning the Darley Irish Oaks
A daughter of the 2009 Derby and Arc winner Sea The Stars, she was unraced at two but after two wins at listed level at Newbury, she came to the Curragh for the Group 1 Darley Irish Oaks and under a supremely confident ride by James Doyle, she came from last to first under hand riding to beat the Epsom winner Forever Together. She went on to win the Group 1 Yorkshire Oaks in similarly impressive fashion before narrowly failing to catch Enable in the Prix de L'Arc de Triomphe on October. The race was to be her aim again this year.
Speaking to the Racing Post on Monday, Haggas said: "The reason for colic surgery on Sea Of Class in the first place was to remove an abdominal mass sitting between the spleen and liver which had intertwined with her gut. That mass was removed and some of the gut taken out.
"However the mass turned out to be a malignant tumour known as a lymphoma. Her surgeon Richard Payne and specialist Celia Marr warned us that lymphoma's can be aggressive and so it proved.
"Having made sure and steady progress under the excellent veterinary team at Rossdale's she took a turn for the worse at 4.30am this morning and a subsequent scan revealed another tumour the size of an orange. Despite regular scans during her convalescence, this was the first sign of an abnormality.
"She was quiet and uncomfortable today – and quite weak and the decision to put her to sleep was then taken unanimously by her team of experts, Maureen and I.
"Owner Mrs Tsui has been in full support of all decisions taken and she, her family and advisors are all devastated. For all of us here, we mourn the loss of the best filly we had anything to do with but will cherish the memories for ever."
7 races - 4 wins
Gr 1 Irish Oaks
Gr 1 Yorkshire Oaks
Gr 1 Prix de l’Arc de Triomphe
Over £1.5 million in prize money