<p>Solid-state spin defects, such as color centers in diamond, are among the most promising candidates for scalable and integrated quantum technologies. In particular, the good optical properties of silicon-vacancy centers in diamond, combined with naturally occurring and exceptionally coherent nuclear spins, serve as a building block for quantum networking applications. Here, we show that leveraging an ultra-high-strained silicon-vacancy center inside a nanodiamond allows us to coherently and efficiently control its electron spin, while mitigating phonon-induced dephasing at liquid helium temperature. Moreover, we indirectly control and characterize a ¹³C nuclear spin and establish a quantum register. We overcome limited nuclear spin initialization by implementing single-shot nuclear spin readout. Lastly, we demonstrate coherent optical control with GHz rates, thus opening a potential connection of the register to the optical domain. Our work paves the way for future integration of quantum network registers into conventional, well-established photonics and hybrid quantum communication systems.</p>