The Liberty X and Big Reunion star told ITV's Lorraine that her two-year-old daughter Faith had adapted to the role of big sister easily, even if she does think little Aaron is a doll at times.
"Faith has been incredible, such a great big sister," said Michelle. "She's been so amazing, so loving towards him. [There have been a] couple of slaps on the head to try to wake him up, but she's really been brilliant... She keeps trying to feed him with her dolls' bottles!"
Singer Michelle and husband Hugh Hanley welcomed Aaron, their second child, on 28 February.
It was particularly poignant for them as they'd been unsure they could expand their family following Faith's birth in January 2012, as Michelle is a carrier of the BRAC2 gene, which can increase the risk of breast and ovarian cancer.
She underwent a double mastectomy in 2012 and has said she will get her ovaries removed.
Michelle told Lorraine Kelly: "We just didn't know [if we'd have another child] because with the BRCA2 gene I have, getting my ovaries removed is something that's going to happen. We didn't know when, it's really hard to say when that should happen; there is no right answer.
"I suppose the longer you leave it, the higher the risk you'll get ovarian cancer, so we were contemplating not having any more children. Baby Aaron was bit of a surprise. We felt it was God's way of saying, 'Have one more then move on with the operation.'"
"I'm blessed," she added. "I know how lucky I am, I really do."
Michelle said she's now aiming to have her ovaries removed as soon as possible, although she has been advised to wait a couple of months after giving birth to allow her hormones to settle.
"I don't really know all the answers," she said. "It's a bit scary."
Yesterday, Michelle was named Disney's Celebrity Mum of the Year at an event in London.
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