In the British TV series "Brideshead Revisited", what was Sebastian Flyte's older brother's nickname?

Two young men meet at Oxford. Charles Ryder doesn't come from wealth. His family doesn't have an aristocratic title or a great sum of money. Nonetheless, he becomes friends with Sebastian Flyte, the younger son of Lord and Lady Marchmain. Sebastian is the family's second son and the brother of "Bridey" (Earl of Brideshead), Julia, and Cordelia.

Sebastian will throw up in Charles's college room through an open window. He then invites Charles to lunch after his teddy bear Aloysius "refuses to talk to him" unless he (Sebastian) is forgiven. The pair quickly develop a very close friendship that borders on a romantic relationship. Charles soon becomes involved with Sebastian's entire family, Catholic peers of the realm in Protestant England.

In the entire series, Bridey (the Marquess's heir) only holds the courtesy title Earl of Brideshead. He follows his mother's strict Roman Catholic beliefs, and once aspired to the priesthood. He is however unable to connect in an emotional way with most people, who find him cold and distant. His actual Christian name is never revealed.

With the 1981 television series of "Brideshead Revisited", it is told in a flashback as Charles, now an officer in the British Army, is moved with his company to an English country house that he discovers to be Brideshead. The house is Sebastian's family home where Charles has good and bad memories of his youth and young manhood, his loves, life, and a journey of faith and anguish.