Rosenberg, who has not been accused of wrongdoing, expressed shock over the allegations reported last week by The Boston Globe.
Senate leaders said yesterday they want to see the Senate Ethics Committee look out of state for an investigator in its probe of Sen. Five days later, the Senate has a different leader.
"I am confident that Senator Chandler will perform the duties of Acting Senate President with integrity and professionalism during this unexpectedly tumultuous time", Cyr added.
Rosenberg announced earlier Monday he would take a leave of absence from his responsibilities as Senate president during the investigation.
Immediately, other senators, as well as Gov. Charlie Baker and Attorney General Maura Healey, called for an independent investigation into Hefner's actions, and Rosenberg's possible role.
"I support the investigation by the Senate Ethics Committee to determine if Stan Rosenberg violated any rules of the Senate, and I am encouraged by the intent to hire an outside investigator". She is the second woman to be Massachusetts Senate president, following Therese Murray, who served until 2015. The investigator would be given the authority to summon witnesses and have access to Rosenberg's office.
Members met in closed-door caucus for hours Monday, deciding the future of the Senate just steps away from the president's office - and on a hall lined with portraits of former Senate presidents.
On Friday, Sen. Barbara L'Italien, an Andover Democrat, began the calls for Rosenberg to temporarily step aside, saying in a statement that anyone with information needs to feel safe coming forward.
Whether that firewall stood up should also be part of the investigation, said Sen.
Rosenberg, he said, is innocent until proven otherwise.
"I thank my colleagues for providing this opportunity and have every confidence that the Acting President will help the Senate focus on a robust agenda for 2018", he said.
Chandler will continue in the post through the course of an investigation into Rosenberg and his staff. Chandler said she is not interested in serving in the post after the investigation.
The ethics investigation will be looking into whether Rosenberg broke chamber rules, if he knew about Hefner's behavior and if the spouse had any influence in the government business.
Several men told the Globe that Hefner sexually assaulted or harassed them, including three men who said Hefner grabbed their genitals. The Gloucester Republican agreed that it could make victims more likely to come forward.
"Sexual assault is a crime", the prosecutors said, "and we want to send a clear message that harassment and assault of any kind will not be tolerated".