UPDATE, 3:25 pm: It's official. Mayor Nutter just announced that his chief of staff, Clay Armbrister, is leaving City Hall.
"This week will always have a little bit of bittersweet to it," Nutter said. "He is out front when he needs to be, but I have never met a more selfless person."
Director of policy Suzanne Biemiller will serve as interim chief of staff.
ORIGINAL POST: PhillyClout sources say that Mayor Nutter's loyal Chief of Staff Clay Armbrister is poised to today announce plans to leave the administration.