Obligatory is the fourth foal of the stakes winner Uno Duo (Macho Uno) and a half-sister to the minor winner Napier (Midnight Lute).

Second dam Willstar (Nureyev), a winner in France, bred six winners. The best of them is Etoile Montante (Miswaki), winner of the Gr.1 Prix de la Forêt and dam of the Group 2 winner Starformer; another, the Listed-placed Starfan (Lear Fan), produced Glaswegian, a Group 3 winner in France. A further daughter of Willstar is the second dam of Country Grammer, winner of the Gr.1 Dubai World Cup in 2022.

Third dam Nijinsky Star (Nijinsky) never raced but produced three stakes winners. Among them is Viviana (Nureyev), a full sister to Willstar, who won at Listed level and was Group 3-placed in France. Viviana is the dam of the seven-time Grade 1 winner Sightseek (Distant View) and the dual Grade 1 winner Tates Creek (Rahy), the second dam of the dual Classic winner Special Duty and the third dam of Expert Eye, a Group 1 winner now at stud. Another daughter, Hometown Queen (Pleasant Colony), was a Grade 1-placed stakes winner and bred Bowman's Band, a Grade 2 winner and sire, while she is also the second dam of the Grade 2 winner and sire Pollard's Vision. A further daughter of Nijinsky Star features in the pedigree of Bonny South (Munnings), a multiple graded winner and multiple Grade 1-placed.

Fourth dam is the Hall of Famer Chris Evert (Swoon's Son), the 1974 champion among three-year-old fillies and a triple Grade 1 winner. She had only five foals, all fillies, and one of them, a stakes winner, became the dam of the champion and sire Chief's Crown (Danzig).

Uno Duo has a two-year-old colt by Arrogate named Treble Clef and a yearling filly by Into Mischief.