Audio decoder for decoding an encoded stereo audio signal, the encoded stereo audio signal comprising an encoded first combination signal generated based on a combination rule for combining a first channel audio signal and a second channel audio signal of a stereo audio signal, the encoded first combination signal being a real-valued modified discrete cosine transform, MDCT, representation of a downmix signal generated by mid/side coding as the combination rule, an encoded prediction residual signal being an MDCT representation, and bitstream data comprising a complex prediction coefficient and a prediction direction indicator, the audio decoder comprising: a signal decoder for decoding the encoded first combination signal to obtain a decoded first combination signal being a decoded downmix signal, and for decoding the encoded prediction residual signal to obtain a decoded residual signal; and a decoder calculator for calculating a decoded stereo audio signal having a decoded first channel signal being a left channel signal of the decoded stereo audio signal, and a decoded second channel signal being a right channel signal of the decoded stereo audio signal using the decoded residual signal, the complex prediction coefficient, the decoded first combination signal, and the prediction direction indicator indicating a prediction direction from a mid signal to a side signal or from a side signal to a mid signal, wherein the prediction direction indicator is a bit in the bitstream data, wherein the decoder calculator is configured for: generating a complex downmix signal from the decoded first combination signal, multiplying (1160b,c) the complex downmix signal and the complex prediction coefficient to obtain a result, adding (1161a,b) the result and the decoded residual signal to obtain an inversely predicted signal, performing an inverse mid/side coding, wherein, in a first state of the prediction direction indicator, the decoded downmix signal represents the mid signal of the inverse mid/side coding and the inversely predicted signal represents the side signal of the inverse mid/side coding, and wherein, in a second state of the prediction direction indicator, the decoded downmix signal represents the side signal of the inverse mid/side coding and the inversely predicted signal represents the mid signal of the inverse mid/side coding, and performing an inverse MDCT, IMDCT, to a result of the inverse mid/side coding to obtain the left channel signal of the decoded stereo audio signal and the right channel signal of the decoded stereo audio signal. a signal decoder for decoding the encoded first combination signal to obtain a decoded first combination signal being a decoded downmix signal, and for decoding the encoded prediction residual signal to obtain a decoded residual signal; and a decoder calculator for calculating a decoded stereo audio signal having a decoded first channel signal being a left channel signal of the decoded stereo audio signal, and a decoded second channel signal being a right channel signal of the decoded stereo audio signal using the decoded residual signal, the complex prediction coefficient, the decoded first combination signal, and the prediction direction indicator indicating a prediction direction from a mid signal to a side signal or from a side signal to a mid signal, wherein the prediction direction indicator is a bit in the bitstream data, wherein the decoder calculator is configured for: generating a complex downmix signal from the decoded first combination signal, multiplying (1160b,c) the complex downmix signal and the complex prediction coefficient to obtain a result, adding (1161a,b) the result and the decoded residual signal to obtain an inversely predicted signal, performing an inverse mid/side coding, wherein, in a first state of the prediction direction indicator, the decoded downmix signal represents the mid signal of the inverse mid/side coding and the inversely predicted signal represents the side signal of the inverse mid/side coding, and wherein, in a second state of the prediction direction indicator, the decoded downmix signal represents the side signal of the inverse mid/side coding and the inversely predicted signal represents the mid signal of the inverse mid/side coding, and performing an inverse MDCT, IMDCT, to a result of the inverse mid/side coding to obtain the left channel signal of the decoded stereo audio signal and the right channel signal of the decoded stereo audio signal. generating a complex downmix signal from the decoded first combination signal, multiplying (1160b,c) the complex downmix signal and the complex prediction coefficient to obtain a result, adding (1161a,b) the result and the decoded residual signal to obtain an inversely predicted signal, performing an inverse mid/side coding, wherein, in a first state of the prediction direction indicator, the decoded downmix signal represents the mid signal of the inverse mid/side coding and the inversely predicted signal represents the side signal of the inverse mid/side coding, and wherein, in a second state of the prediction direction indicator, the decoded downmix signal represents the side signal of the inverse mid/side coding and the inversely predicted signal represents the mid signal of the inverse mid/side coding, and performing an inverse MDCT, IMDCT, to a result of the inverse mid/side coding to obtain the left channel signal of the decoded stereo audio signal and the right channel signal of the decoded stereo audio signal.