Looks like he got 11 - 10 for the killing plus an extra year for drugs offences.
As has been said, he is all but automatically entitled to a discount of up to a third for pleading guilty, so 10 is about right.
A defendant who pleads not guilty and is convicted after a trial is not entitled to the discount so could, in theory, get close to the maximum.
The judge in this case clearly saw it as one of the most serious because his sentence calculation must include the discount.
In other words, the judge would have given the defendant a lot more had he pleaded not guilty and been convicted after a trial.