Thundering On will attempt to become the 17th filly to complete the English-Irish Oaks double when she returns to competition against 3-year-olds at the Curragh on Saturday.
The Joseph O’Brien-trained filly meets 10 rivals in the €500,000 Group 1 Irish Oaks over 2400 meters, three weeks after finishing fourth against older fillies and mares in the Pretty Polly Stakes.
Masaka became the first filly to win both Oaks races in the same season in 1948, while Minnie Hauk was the 16th and most recent to complete the double last year.
Victory for Thundering On would give O’Brien and jockey Dylan Browne McMonagle their first Irish Oaks wins, while Frankel would sire the winner for a second straight year following Minnie Hauk’s success.
Thundering On produced a commanding performance at Epsom on June 5.
Held up near the rear, she made rapid progress in the straight before drawing 3 3/4 lengths clear under McMonagle on good-to-soft ground.
Her return to the Curragh produced a different result. Dropping to 2000m on good-to-firm ground, the daughter of Frankel finished fourth, 2 1/2 lengths behind Estrange in the Pretty Polly.
A post-race veterinary examination also found Thundering On to be coughing.
She returns to the distance of her Epsom victory on Saturday, although the Curragh surface was listed as good to firm on Friday. McMonagle remains aboard the winner of two of her six starts.
O’Brien also fields Royal Ascot runner-up Johanna Walsh and unbeaten supplementary entry Rebel Moon, giving him three of the 11 runners.
Johanna Walsh was denied in the final strides of the Group 2 Ribblesdale Stakes, losing by a head to Earth Shot over a similar distance to Saturday’s race.
The daughter of Sea The Stars had won a Leopardstown maiden on her previous appearance and will be ridden for the first time by Colin Keane.
Rebel Moon makes her Group 1 debut after winning both of her starts.
The Lope De Vega filly followed a debut victory with success in last month’s Group 3 Jannah Rose Stakes at Naas. Her connections paid €50,000 to supplement her for the Irish Oaks, where she will race beyond 2100m for the first time.
O’Brien told the Racing Post: "Thundering On has been in good form since the Pretty Polly and we’ll be watching the weather.
"Johanna Walsh had a really good run in the Ribblesdale and we're looking forward to the weekend with her. Rebel Moon had a real nice run at Naas.
"The form has been franked and we’re looking forward to seeing what she can do going up to a mile and a half."
French Oaks third Inis Mor and unbeaten Munster Oaks winner Sparan Nua were also supplemented for €50,000.
William Haggas sends out Earth Shot, who has two wins and two seconds from four starts and will make her first appearance at Group 1 level under James Doyle.
The Wathnan Racing-owned filly began her season with a five-length maiden victory at Newmarket before losing by a head to Inis Mor in the Height of Fashion Stakes at Goodwood.
Earth Shot then stepped up to about 2400m at Royal Ascot and finished strongly to catch Johanna Walsh in the Ribblesdale.
Haggas is one of three trainers represented on Saturday who has previously won the Irish Oaks, having combined with Doyle and Sea Of Class in 2018.
Inis Mor followed her Goodwood victory with a close third behind Diamond Necklace in the Group 1 Prix de Diane at Chantilly.
The David Menuisier-trained filly will try 2400m for the first time, having made her previous seven starts over distances ranging from 1400m to 2100m.
Menuisier, like Joseph O’Brien, is seeking his first victory in the race.
Sparan Nua has won all three of her starts for Jim Bolger and is already proven over the Irish Oaks distance.
The daughter of Dawn Approach progressed from maiden company to win the Group 3 Munster Oaks at Cork last month and now steps into Group 1 company under Declan McDonogh.
Bolger is seeking his third Irish Oaks victory after winning with Give Thanks in 1983 and Margarula in 2002.
Eight of Saturday’s 11 runners are trained by members of the O’Brien family, with Joseph’s three fillies joined by five from his father Aidan’s Ballydoyle stable.
Aidan O’Brien is chasing a record-extending ninth Irish Oaks victory after Minnie Hauk supplied his eighth last year.
He has won three of the past five editions, taking the race with Snowfall in 2021, Savethelastdance in 2023 and Minnie Hauk in 2025.
Ryan Moore partners Cheshire Oaks winner Amelia Earhart, who started favorite at Epsom but weakened late to finish sixth behind Thundering On. She will wear cheekpieces for the first time on Saturday.
Moore has won the Irish Oaks four times. Victory aboard Amelia Earhart would move him to five, one behind Johnny Murtagh’s record of six.
Epsom third Sugar Island also returns in first-time cheekpieces, while Beautify, Cameo and Composing complete Aidan O’Brien’s five-runner team.
First held in 1895, Saturday’s edition is the 132nd running of the Irish Oaks. The race was originally contested over one mile before being extended to its present distance in 1915.
The G1 Irish Oaks (2400m) is carded as S1-7 and will be run at 11.35pm (Hong Kong time) on Saturday, 18 July.
