|The Battle of Tinchebray|
Flambard convinced Duke Robert that he should assert his claim to the throne (despite Robert's agreement to not pursue it in exchange for 3000 marks/year). With Flambard organizing the fleet, Robert's army landed in England in July 1101. It didn't go well. Henry's army was larger, and England didn't really want another change on the throne, so the local support was all for Henry.
Within a couple weeks of landing, on 2 August, Robert and Henry agreed to the Treaty of Alton—Alton was where Henry's army met and stopped the advance of Robert's—in which Robert (again) agreed to renounce any claim to the throne of England in exchange for an annual payment. Flambard, no doubt part of the negotiating force, actually got reinstated as Bishop of Durham! But he chose to stay in Normandy for five years: Robert had thanked him for his help by granting him the see of Lisieux
In 1105, however, Henry broke the agreement. Despite the Treaty of Alton, Henry invaded Normandy and fought against his brother in the Battle of Tinchebray. Robert was captured and imprisoned (he died in 1134, in Cardiff Castle). After the battle, Flambard made his peace with Henry, returned to England, and took up responsibility for Durham again.
Back in England, Flambard continued major building projects: a cathedral, a defensive wall around Durham Castle, Norham Castle, and more. He died on 5 September 1128.