Little Dorrit ending?

[ginevragirl]

I just finished watching Little Dorrit and I absolutely loved every minute of it, but I found myself extremely confused by the ending. Can anyone explain the specifics of the huge massive secret that Mrs. Clennam had been hiding? Lol. I just didn't understand it.

And on a different note, I have loved Russell Tovey since I found Being Human, but I think I love him even more after watching him in this. I thought he was fantastic. :)