(CNN) - CNN has learned the negotiations that led to Mitt Romney's endorsement of John McCain included a prominent role by John Weaver, who was the Arizona senator's top political strategist until he left in a campaign shakeup last summer.
According to several sources familiar with the talks, Weaver got involved with the blessing - indeed at the urging - of two current top McCain advisers: Charlie Black and Steve Schmidt.
Both were aware of Weaver's friendship and past working relationship Romney campaign manager Beth Myers. Weaver and Myers worked together on a Texas campaign and at the Texas State Republican Party back in the 1980s and have remained good friends.
According to sources in both the Romney and McCain camps, Weaver made contact with Myers last week to initiate talks aimed at winning Romney's endorsement and an appeal from him to his delegates to rally to McCain's candidacy.
A source involved in the internal Romney deliberations confirmed Weaver's role, and said the governor came to the conclusion his endorsement was important now to send a signal he believes it is time for the party to unite behind McCain and focus on a difficult fall election environment.
Programming note: Watch Larry King’s exclusive interview with GOP front-runner John McCain tonight on Larry King Live at 9 P.M. Eastern.
–CNN Chief National Correspondent John King