The high number of cyber threats poses significant challenges, with impactful software exploits ranging from data theft to ransomware deployment. Unfortunately, past research highlighted limited security expertise within development teams. Collaboration between developers and security experts, therefore, emerges as one of the few workable means to address this gap. In this paper, we explore the complex interplay between developers and security experts within Scrum, one of the most widely adopted frameworks which actively promotes collaboration, to shed light on their working relationship, challenges, and potential avenues for improvement. To this end, we conducted a qualitative interview study with 14 developers and 13 security experts. Our qualitative results reveal three communication patterns and five shared challenges between the groups affecting the develop-security expert collaboration. Top challenges include consistent interaction difficulties and the lack of workable means to balance business and security needs. As a result, we found that three core Scrum values (openness, respect, courage) are missing from this relationship. Based on our results, we propose recommendations for fostering a healthy collaboration between developers and security experts, both within and beyond Scrum.