ID Please

This seedling appeared a couple of weeks ago.  I'm wondering if it's a herb - maybe a basil - I sowed seeds in this patch last year but before they had all come up, I decided to plant something else.  This lone plant has appeared.  If you rub the leaves, they do have a herby smell but not clearly identifiable.   Does this look as if it could indeed be a basil?  I'm reluctant to pull it as it seems to be happily growing.  And I'm a sucker for something which seems to have found a place for itself and seems to want to be there!  (The nettle like flowers are actually lilac - I'm struggling with the manual settings on this bridge camera and as it was dull I tried to compensate with the lighting - but made a mess of it from the colour point of view).  The plant is 5" high .