EXCLUSIVE

WWE star Rusev might be a tough guy in the ring but he's a softie for his real-life girlfriend Lana ... because he asked her to marry him.

Sources close to the couple tell TMZ Rusev proposed to his WWE manager gf last month at their Nashville home. We're told Rusev proposed in the couple's swimming pool and filmed the whole thing.

Judging by the size of the rock ... we're guessing it was pretty easy for Lana to say yes.