Since 82, Liu Qing, Zhang's son from his concubine Consort Song, had been the designated heir, secured from the favor of Empress Ma. However, Ma's death in 79, made Lady Dou the empress, and—aiming to develop her family's power—she adopted Prince Zhao, with the intention of instilling him as heir. As a result, when Consort Song became ill in 82 and asked for herbs, Empress Dou falsely accused her of planning to use the herbs for witchcraft against Zhang. Dou then ordered Cai Lun to interrogate Consort Song and her sister, another imperial consort, in order to force a confession; they both killed themselves. Believing Dou's accusation, Zhang replaced Liu Qing with Prince Zhao as heir.