Britney Spears’ ex-husband — not Kevin Federline, the other one — is back in her life and seems to be shooting his shot for another chance … he’s joining the #FreeBritney movement.

Jason Allen Alexander — who you may recall was married to Britney for a whopping 55 hours after their wild, 2004 Vegas wedding — was outside the L.A. courthouse Wednesday where a hearing took place over her conservatorship … which has been in force since 2008 after her breakdown.

Jason reps himself as a bit of an expert on these conservatorship court proceedings — though it’s unclear why — and tells us he believes it’s long overdue for her to be rid of it … much like thousands of other Britney fans.

More interesting though, is Jason says he’s back in touch with his longtime friend and brief spouse after not hearing from her for a decade … and suggests he’s been heavily involved in major recent developments in her life.

Jason even admits he’s there with the hope of rekindling things with Britney — claiming their marriage was never given a fair chance … and he’s down for a do-over.

As we reported … Britney’s looking to make some big changes to her conservatorship — mainly, she wants her father, Jamie, to no longer be in charge of it.

As we reported, sources with direct and long-standing knowledge of the conservatorship tell 360aproko … Britney’s in a conservatorship because she’s not capable of making important life decisions because of her mental illness. They also say if left to her own devices things could go south very fast.