Victorian Premier Jacinta Allan says she was shocked when her predecessor and friend Daniel Andrews phoned her to say he was leaving.
Mr Andrews resigned on Tuesday afternoon after almost nine years in the top job and winning three elections for Labor.
He called Ms Allan, then his deputy, to let her know of his decision.
"I was shocked, I was shocked," she told reporters at Pakenham on Thursday.
"I'll miss him, he's been a tremendous friend. He is a tremendous friend and a wonderful, wonderful colleague.
"So, yeah, I was surprised to get that call."
The pair have known each other since the 1990s, are both members of Labor's socialist left faction and sat in parliament together for more than 20 years.
Ms Allan was sworn in as Mr Andrews' replacement on Wednesday evening with leadership hopeful Ben Carroll appointed as her deputy.
