She was out of Jersey Lightning, who goes back to Longfellow through his Kentucky Derby-winning son, Riley.

Regret was also the first undefeated horse to win the Kentucky Derby, and had only three starts prior to the race (matched by Big Brown in 2008).

[1] 1915 was the year of the Triple Crown fillies, as Rhine Maiden won the Preakness Stakes.

After the 1917 racing season, Regret was retired for breeding to the new Whitney farm in Lexington, Kentucky.

In this last season, she raced in the Brooklyn Handicap against the best of her generation: Old Rosebud, Roamer, Omar Khayyam (winner of the 1917 Kentucky Derby), Boots, Ormsdale and Chiclet.