Shah Jahan had planned to construct another Taj Mahal in black marble on the other side of the river, but the war with his sons interrupted his plans.

Shah Jahan had planned to build mirror image of the Taj Mahal he built for Mumtaz, albeit in black, on the other side of the river and connect the two by a bridge. This Black Taj was to be dedicated to Shah Jahan himself. A European traveler by the name of Jean Baptiste Tavernier who visited Agra in 1665 first mentioned the idea of Black Taj in his fanciful writings. And considering Shah Jahan's obsession with symmetry, the idea certainly seems plausible. More credibility to the story is added by an observation made by archeologists in 2006, when they reconstructed part of the pool in the moonlit garden and it reflected a dark reflection of the white mausoleum. The writings of Tavernier mention that Shah Jahan began to build his own tomb on the other side of the river but could not complete it as he was deposed by his own son Aurangzeb.
Fuel to the fire is further added as some scholar suggests that the blackened marbles in Mehtab Bagh that lie on the other side of the river are actually grim remains and foundations of an abandoned plan.