The heir apparent is already in line to fill the soon-to-be vacated seat of longtime state Sen. John Cullerton.

Within hours of Cullerton’s shocking announcement at the end of the fall veto session in Springfield Thursday that he plans to retire in January, signs were already pointing to state Rep. Sara Feigenholtz to replace her fellow North Side Democrat in the Illinois Senate.

Feigenholtz — who worked as Cullerton’s district chief of staff for more than a decade dating back to his time in the Illinois House of Representatives before she was first elected in 1994 — said Saturday she has contacted Democratic ward committeemen who will eventually vote to appoint Cullerton’s replacement once he steps down.

“I learned a great deal from John,” she said. “He’s been a great mentor, and we’ve had a great working relationship meeting the needs of the community together.

“But I’m excited to go on another adventure,” said Feigenholtz, whose 12th House District encompasses the lakefront half of Cullerton’s 6th Senate District. “I feel like I can be as or more impactful in the Senate compared to the House. But it’s a seismic shift with him not being there. It’s the end of an era, and he walks out on his own terms with his head held high.”

Feigenholtz said she was as stunned as anyone by Cullerton’s bombshell end-of-session announcement, ending a legislative career that has spanned four decades. She said her first call was to state Rep. Ann Williams, whose 11th District covers the western half of the Cullerton’s Senate district.

Williams, the only other obvious candidate to potentially seek the Senate appointment, threw her support behind Feigenholtz to become Cullerton’s replacement.

“The three of us have been a really strong team. Sara brings so much to the table and she puts 100% of herself into every issue,” said Williams, who added that she wants to see things through as the recently appointed chair of the House Energy and Environment Committee.

While the successor for Cullerton’s Senate seat seems clear-cut, the race to fill his post as Senate president is poised to be a free-for-all, with a handful of leaders already being floated.

And as for who might eventually take Feigenholtz’s House seat, it’s too soon to say who might eventually land in that portion of the legislative game of musical chairs. Feigenholtz said she’ll still file to run for the House in the March election.

“There is no shortage of committed, educated, politically active folks around here,” she said. “I hope it’s someone who appreciates the diversity of the district.”