Sean gave her a lovely ride and kept filling her up." On her final appearance of the year she finished fifth in the Group 2 May Hill Stakes at Doncaster Racecourse but was only three and a half lengths behind the winner Laurens (later to take the Fillies' Mile). On 18 April Billesdon Brook began her second season in the Nell Gwyn Stakes (a major trial race for the 1000 Guineas) over seven furlongs at Newmarket Racecourse. She appeared to recover from a poor start but never looked likely to win and finished fourth behind the Godolphin filly Soliloquy. On 6 May Billesdon Brook started the 66/1 outsider in a fifteen-runner field for the 205th running of the 1000 Guineas over the Rowley Mile. Happily started favourite while the other fancied runners included Soliloquy, Laurens, Wild Illusion (Prix Marcel Boussac) and I Can Fly. Billesdon Brook raced towards the rear of the field before making a forward move approaching the last quarter mile. She passed at least ten horses in a matter of strides to take the lead a furlong out and won by one and three quarter lengths from Laurens with Happily taking third ahead of Wild Illusion. Her winning odds made her the longest-priced winner in the race's history, eclipsing Ferry's 50/1 success in 1918. Richard Hannon admitted that the filly was not the best fancied of his three runners in the race but insisted that there was "no fluke" about her victory while Levey said "She ran "gassy" in the Nell Gwyn. I thought she’d improve and that if everything fell into place for her she would be in the first four. But I was so happy at halfway and was counting down the horses I had left to pass at the two-furlong marker. I just hoped she would keep running, but she sailed all the way to the line". Levey, who is of Irish and Swazi parentage was described as the first black jockey to win a British Classic Race. At Royal Ascot in June Billesdon Brook started 9/2 second favourite for the Group 1 Coronation Stakes. After being retrained towards the rear of the field she stayed on steadily in the straight but never looked likely to win and came home fourth of the twelve runners behind Alpha Centauri. The filly was then stepped up in distance for the ten-furlong Nassau Stakes at Goodwood and finished fourth again, beaten three and a half lengths by the winner Wild Illusion.