Former Democratic mayors of the two largest cities in Massachusetts are backing Sen. Scott Brown (R-Mass.) over Elizabeth Warren.

Ray Flynn, who served as Boston’s mayor for almost a decade before being named an ambassador under President Clinton, will endorse Brown on Monday at South Boston’s Castle Island. A conservative Democrat, Flynn has long been allied with Brown, and endorsed his 2010 Senate bid against state Attorney General Martha Coakley (D).

Hours later, former Worcester, Mass., Mayor Konnie Lukes will announce her support for Brown in the city Lukes ran until 2009.

Both endorsements serve as reminders of Brown’s continued crossover appeal to centrist Democratic voters, despite the star power and grassroots energy behind Warren’s campaign.

- This post was updated at 10:21 a.m.