Minor adjustment:

$line =~ /
    ^
    (.+?)
    (?:
        <
        (two|three)
        >
    )?
    $
/xs;
[download]

Another approach:

my $pre= $line;
my $post= '';
if(  $pre =~ s/
        \s*
        <
        (two|three)
        >
        $
    //xs
) {
    $post= $1;
}
[download]