Htaccess redirect woes

1

I can’t wrap my brain thoughts around this, haven’t found the correct solution on the webs.

I want to redirect

http://domain.com/subdir1/subdir2

-to-

http://domain.com/subdir1/subdir2/subsubdir

this is an expression engine site, subdir2 doesn’t actually exist in any code form so I can’t place any code anywhere, which is why I must do this in htaccess.

HALP