Wiz Khalifa and Amber Rose sparked rumors of a new romance when pictures of the two surfaced online and they began Tweeting to each other.

Amber Rose has filed for divorce from husband-of-1-year Wiz Khalifa ... and she's gunning for full custody of their kid ... TMZ has learned.

In the divorce docs -- obtained by TMZ -- Amber says they split on Monday and cites irreconcilable differences.

Amber is asking for full legal and physical custody of their 1-year-old son Sebastian. She's willing to give Wiz visitation.

And this is interesting. Amber acknowledges there's a prenup, which you would think would work in Wiz's favor, but she says it's valid ... presumably, she's not challenging it. The docs say the prenup provides spousal support.

As for why they split, there's been a buzz over the last few days of infidelity, but there's no mention of it in the papers.

Sources connected with the couple say the split is bitter.