Montassib is the third foal out of Felwah (Aqlaam), who won four of her seven starts at up to 7½f, and is the best of her four winners.

Second dam Efisio's Star (Efisio) was unraced and has two winners, among them Felwah. She is a half-sister to Lady Gloria (Diktat), winner of two Group 3 races including the Gr.3 Princess Elizabeth Stakes, and to the five-time winner Light And Shade (Aqlaam), third in the Listed Snowdrop Stakes.

The third dam Tara Moon (Pivotal) was unraced.

Tara Moon is a granddaughter of Tadwin (Never So Bold), winner of the Listed Hopeful Stakes and second in the Gr.3 Flying Five Stakes, whose eight winners are headed by Musadif, a Group 3 winner in Norway, and Nadwah, winner of the Queen Mary Stakes, then a Group 3 (both by Shadeed).