This work examines how experiences in one disciplinary domain (biology) can impact the relationship a student builds with another domain (physics). We present a model for disciplinary relationships using the constructs of identity, affect, and epistemology. With these constructs we examine an ethnographic case study of a student who experienced a significant shift in her relationship with physics.We describe how this shift demonstrates (i) a stronger identification with physics, (ii) a more mixed affective stance towards physics, and (iii) more expertlike ways of knowing in physics. We argue that recruiting the student's relationship with biology into experiences of learning physics impacted her relationship with physics as well as her sense of how physics and biology are linked.