The couple has been dating for a while and recent speculation led gossips to believe she had become the former Led Zeppelin frontman's second wife.
But, in a new interview to promote her album American Kid, which features three collaborations with her boyfriend, Griffin insists she's not Mrs. Plant yet.
She tells Billboard.com, "We're not legally married, no."
However, the singer appears to be smitten with the British rock legend, who she says inspires her greatly.
She adds, "We get a lot of energy from each other's singing. We both have similar places that we come from as singers, a lot of emotion, and sometimes the emotion overrides technique. He inspires me. He goes far and deep."