Have you watched the last Naruto Shippuuden episode (72) ?
At the end after the credits and the preview of the next episode there is this special one-minute animation which provides general information... Remember it?
At the very end of this animation 4 jinchuurikis with their bijuus are shown; from right to left are:
Gaara with Ichibi
Yugito with Nibi
Naruto with Kyuubi and
an unknown jinchuuriki with his/her unknown bijuu...
The leftmost jinchuuriki and his/her bijuu are shown in black !!
Who do you think they are?
The "Killer Bee" with the eight-tails??