Melissa Joan Hart pregnant with third child

Melissa Joan Hart revealed the news of her pregnancy on Twitter this morning. Photo / Supplied

Melissa Joan Hart is expecting her third child.

The former Sabrina the Teenage Witch star - who turns 36 today - announced the news on twitter by posting a picture of her visibly pregnant self along with sons Mason, six, Braydon, four, and husband Mark Wilkerson.

She tweeted: "(Early) Happy Birthday to me! And baby makes 3!"

A source told Life & Style magazine the Melissa and Joey star could not be happier about the latest addition to the clan.

The insider said: "She's really excited and is starting to show. You can barely tell, but there's a teeny-tiny little bump."

Melissa - who married 35-year-old musician Mark in 2003 - had always hoped to have a large family, and has even been looking in to the possibility of adoption.

Following the birth of Braydon, she revealed: "We definitely want to add to our family. We're interested in adopting as well. We're just starting to explore that.

"Since I was little, I knew that I wanted to have children. I'm the oldest of eight kids, and I have always liked the idea of a big family."

- Bang! Showbiz