sub last-word( Str $sentence, Regex $matcher ) 
{
    $sentence.words.grep( $matcher ).tail;
}

say last-word( '  hello world', rx/ <[ea]> l /                ); # 'hello'
say last-word( "Don't match too much, Chet!",  rx:i/ ch . t / ); # 'Chet!'
say last-word( "spaces in regexp won't match", rx/ \s re /    ); #  undef