  We give heavy quark-diquark symmetry predictions for doubly heavy baryons and
tetraquarks in light of the recent discovery of the $\Xi_{cc}^{++}$ by LHCb.
For five excited doubly charm baryons that are predicted to lie below the
$\Lambda_c D$ threshold, we give predictions for their electromagnetic and
strong decays using a previously developed chiral Lagrangian with heavy
quark-diquark symmetry. Based on the mass of the $\Xi_{cc}^{++}$, the existence
of a doubly heavy bottom $I=0$ tetraquark that is stable to the strong and
electromagnetic decays has been predicted. If the mass of this state is below
10405 MeV, as predicted in some models, we argue using heavy quark-diquark
symmetry that the $J^P=1^+$ $I=1$ doubly bottom tetraquark state will lie just
below the open bottom threshold and likely be a narrow state as well. In this
scenario, we compute strong decay width for this state using a new Lagrangian
for tetraquarks which is related to the singly heavy baryon Lagrangian by heavy
quark-diquark symmetry.
