First detection of Sgr A* in infrared interferometry: the top panels show the observed squared visibilities and closure phases for a five minute exposure centered on Sgr A* during a flare with a peak brightness of about m_K ≈ 15 mag. The prominent modulation in the two quantities results from the two brightest objects in the field, the flaring Sgr A* and the star S2. The black line is the best fit “binary” model. The middle left panel displays the reconstructed image from the combination of three exposures around the peak of the flare. The middle right panel plots the 3σ detection limits for a third source in the full data set, for which the average flare brightness was m_K ≈ 15.5 mag. We can exclude a third source brighter than m_K = 17.1 mag for 90% of the area. The lower panel shows the H-band (black circles) and K-band (blue triangles) lightcurve of Sgr A* during the flare, as measured from the acquisition camera images and derived from the best fit to the interferometric visibilities and closure phases, respectively.