Peter MacKay officially signalled he's ready to jump into the Conservative leadership race today with a four-word tweet: "I'm in. Stay tuned."

MacKay is expected to formally launch his campaign late next week.

The tweet (which he also sent out in French) publicly confirms work that has been going on behind the scenes for some time.

MacKay has recruited former Conservative MP Alex Nuttall as his campaign manager. Nuttall was an organizer for Maxime Bernier during the Conservative leadership race in 2017.

Michael Diamond, who ran Ontario Premier Doug Ford's PC leadership campaign in 2018, will be MacKay's director of communications.

MacKay will be running to lead the party he helped to create. He took the reins of the Progressive Conservative Party and quickly merged it with Stephen Harper's Canadian Alliance to form the Conservative Party in 2003.

And he may well wind up running against a former political mentor, Jean Charest. The ex-premier of Quebec, who led the federal Progressive Conservative party from 1993 to 1998, is organizing and gathering support while he considers a run at the Conservative leadership.

Meanwhile, CBC News has learned former interim leader Rona Ambrose's supporters presented her this week with an assessment of her chances should she make a run for the party leadership.

Ambrose still deciding

Ambrose will have to weigh enthusiasm among Conservative members for her candidacy against the prospect of having her record in cabinet attacked by opponents.

Multiple sources tell CBC News Ambrose is still considering her options and is expected to make a decision soon.

MacKay and MP Marilyn Gladu are the only Conservatives to date to publicly signal leadership runs. Gladu is the only caucus member to declare so far, but her colleagues Erin O'Toole and Pierre Poilievre are widely expected to announce soon.

Charest is reportedly close to a decision on a possible leadership run, as is MP Michael Chong, who ran in 2017.