Sam Lutfi — who notoriously served as Britney Spears’ “manager” during her famous breakdown — is at the center of another ugly celebrity imbroglio.

We’re told that Lutfi has been using tough-guy tactics to try to strong-arm Isaiah Silva — the estranged husband of Kurt Cobain and Courtney Love’s daughter, Frances Bean — into returning her father’s guitar, which the rocker played in Nirvana’s legendary “MTV Unplugged” session and which is said to be worth millions. Frances gave it to Silva as a wedding gift.

Bizarrely, sources say that part of the sketchy scheme cooked up by Lutfi — who has been a confidant of Love’s for several years — is to threaten Jessica Sullivan, 27, the mother of Silva’s 7-year-old child, Arlo, apparently in an attempt to get her to side with Frances in the upcoming divorce proceedings, in which the guitar will be the headlining act.

During their marriage, which lasted from June 2014 until they split in March 2016, Frances and Silva purchased a home in West Hollywood, Calif., for Sullivan and Arlo, so they could live close to Silva. In his calls, Lutfi threatens to evict them if they don’t cooperate.

In one call, Lutfi tells Sullivan that Frances would “take care” of Sullivan and her family “until the day [she] dies” if she took Frances’ side. But in a frightening tirade, he then threatens to make sure Arlo ends up in an orphanage, and promises that he would “put away” Sullivan and Silva if they didn’t cooperate.

In the exchanges, Lutfi calls Sullivan a “whore” and a “c - - t,” and in text messages provided to us, oddly, by Lutfi himself, he says ominously, “You are done! You sick bitch,” and calls her a “white trash con artist.”

Lutfi told Page Six he lost his temper with Sullivan because she had upset Frances and because he felt threatened by her. “[Jessica] recently tried to provoke Frances into killing herself by taunting her about her father’s suicide,” said Lutfi, calling Sullivan “an awful human being.” “So I told her off,” he said.