Updated 4:36 p.m.

Mayor Kenney announced on Wednesday morning that Jane Slusser, his chief of staff from the beginning of his term, is set to resign next week. In her place, another Kenney staffer is due for a promotion.

The announcement came as a huge surprise. Slusser, a Billy Penn Who’s Nexter, has been with Kenney ever since his 2015 bid for mayor — back then, she was an integral part of his campaign. As chief of staff, she’s played a major role in the implementation of the soda tax and the update to the city’s sexual harassment policy.

Effective Aug. 10, Deputy Mayor for Policy and Legislation James Engler will succeed Slusser as Kenney’s chief of staff.

So who’s that guy? Here’s a quick rundown:

Engler is another Billy Penn Who’s Nexter. In his current role, he’s basically the middleman between the Mayor’s Office and City Council. That means he’s been central to getting passed Kenney’s legislative priorities, like the soda tax and the related Rebuild program. He’s also been responsible for overseeing Philadelphia Gas Works.

Engler and Kenney go way back.

Before all his current stuff, Engler was the policy director for Kenney’s 2015 campaign, and before that he was the legislative director for Kenney back when he was on City Council. Engler’s priorities then were decriminalizing marijuana, reforming building safety regulations and protecting undocumented immigrants.

In 2015, when Kenney first hired Engler to his current role, Council President Darrell Clarke was a big supporter.

“Jim Engler is not the most well known name in Philadelphia, but his work has affected the lives of thousands in this city,” Clarke said in a statement. “From saner marijuana regulations to more robust demolition and construction safety rules, Engler’s compassion and intelligence have enabled better public policy in the City of Philadelphia.”

Engler did his undergrad at Villanova, then went on to Temple’s Beasley School of Law.

As for Slusser — she said in a statement on Wednesday that she won’t be involved in Kenney’s 2019 bid for reelection. Instead, she’s moving on to a new role focused on “mobilizing voters” in advance of the November midterm elections. We don’t know exactly what that means — but she promised to give more details once she’s officially done serving Philly.