Astrometric analysis of GJ 758 B, showing its position and implied northwest motion relative to the primary, since its discovery in 2009-05. The black markers are from previous astrometry, and the blue markers are from the four epochs of detection presented in this work, all with associated error bars displayed. The predicted motion (due to GJ 758's proper motion and annual parallactic motion) of the background star discovered in 2009-08 is shown as a black curve, turning cyan at our first observing epoch in 2012-06. The star was in our FOV, nearing the edge of our detector (marked with a red dashed line) for the last two epochs, but too faint to be detected.