Dean Fuleihan, a 33-year veteran of the Assembly who has served as Sheldon Silver’s right-hand man – if not an outright extension of his brain – for the entire duration of his speakership (which started in 1994), is departing his post at the end of the month, multiple sources confirm.

A formal announcement will be made by the speaker at the Assembly Democrats’ closed-door conference later today. Fuleihan is not leaving for another job. But he’s also not retiring and is considering a number of options, I’m told.

He’ll likely keep his hand in government, but is not yet sure about his next move.

Silver will also be announcing internal shuffling to fill the considerable gap that Fuleihan will leave behind. The new team – and there will be more than one person stepping up to take over Fuleihan’s duties – will include the elevation of Matt Howard, who has helped Fuleihan with budget negotiations over the past decade.

I can’t really overstate the significance of this. The news will undoubtedly send shockwaves through the Capitol. (Actually, that has already started as word of Fuleihan’s imminent last day is starting to leak out).

For as long as I have covered Albany, there was Dean and there was Shelly. The concept of the Assembly majority without Fuleihan is going to take some getting used to.

Fuleihan started working for the Assembly back in 1978 under then-Speaker Stanley Steingut. Fueled on endless cups of coffee and the ability to function at high levels on very little sleep, he has been the Assembly Democrats’ point man in every budget negotiation I can remember, and I’ve been covering the Capitol on and off since about 2000.

Fuleihan has remained a constant in Silver’s inner circle even as other high-profile members departed (Pat Lynch, communications director) or were felled by scandal (Michael Boxley, counsel). But he has been talking about leaving for several years – at least since the 2008 elections when Silver faced – and handily won – his first primary challenges in two decades.

Silver and Fuleihan have been quietly laying the groundwork for this for some time now, insiders say. That’s part of the reason why the speaker brought in former state Supreme Court Justice Jim Yates (who was appointed a Court of Claims Judge by then-Gov. Mario Cuomo in 1992) to serve as his counsel at the start of this year.

Fuleihan agreed to stay on through this budget battle to help the speaker navigate the twin challenges of a fiscal crisis and an uber-aggressive new governor. Now that the budget has been passed – on-time for the first time in five years – he has held up his end of the bargain.

This departure will undoubtedly reignite speculation about Silver’s own tenure. He is longest-serving member of the Capitol’s power trio, although he has not yet hit the longest-serving speaker in history mark.

Sources insist Silver will not be following Fuleihan out the door any time soon, despite the fact that he appears to have lost some clout in the Cuomo Capitol. Silver loyalists remind anyone who suggests the speaker’s time in power might be winding down that he is waiting game master. Further complicating matters is the fact that he has no clear successor.