she's in for a shock

my mum has 4 grandchildren 3 from my sister + 1 from me and she turned around today after looking at at their baby photos and said " im happy with the amount of grandchildren I have" well lovely mummy dearest get ready to be extra happy with another because if all goes to plan #5 will be joining the clang this year. she doesn't know we are TTC and I don't intend on telling her because I don't want people having a say so soon I want it to be a private moment for myself and my SO, I know she'll be happy as anything but she's in for a really big shock.