The Oscar-winning star, who celebrated the singer's 30th birthday in Venice, described motherhood as the ultimate "blessing".
"I think motherhood is the biggest blessing of all time and it gives your life real meaning. It's always interesting when you're a woman with success and you've achieved a lot, and then you have a baby and you realise everything you thought was an achievement really is nothing until you have a kid," she told Entertainment Tonight.
"I think that that will be her experience, and it's wonderful to see her so happy right now, and so looking forward to the experience. I'm very happy for them."