Octavia Spencer is saying sorry to Britney Spears and Sam Asghari ... she acknowledges her prenup comment on their engagement announcement wasn't funny.

The Oscar-winning actress says she was just trying to make a joke when she left a comment on Britney's social media post saying, "Make him sign a prenup" ... and she says she's since privately apologized to both Britney and Sam.

Octavia says her "intention was to make them laugh not cause pain" ... and now she hopes to "restore just a smidge of happiness they were robbed of."

The actress wasn't alone in telling Britney to get a prenup ... and as we reported, Sam told fans almost right away he would sign a prenup alright ... joking the prenup would be designed to protect his Jeep and shoe collection.

Octavia's singing a different tune in the wake of her apology ... she says she's thrilled for Britney and thinks the singer has found happiness after going through a lot of pain.

But, here's the real story ... Britney IS getting a prenup, because our sources say literally a day after she got engaged her team was on the case.

No word if Octavia's getting a wedding invite.