A regular expression

Ask for help. A regular expression
The string that needs to be matched is: bbabbbbabc11
I want to match the ABC11 to the back.
With a (. +?) 11, it will match to ABBBBABC11.

Because the characters in a and 11 are indeterminate in length, just want to match the last one, what is the best way to use a regular word?
------to solve the idea----------------------

var str= "Bbabbbbabc11";

var reg=/a[^a]*11/;

Alert (reg.exec (str));

------to solve the idea----------------------

$s = ' bbabbbbabc11 ';
$p = '/a[^a]+11/';
Preg_match ($p, $s, $m);
Print_r ($m);

Array
(
    [0] = Abc11
)

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