Supermodel Hunter, who has two children, LIAM, 11, and RENEE, 13, with Stewart insists she was delighted when Lancaster gave birth to his son Alastair Wallace in November (05).
She says, "Penny and I get on - and it's genuine, not just for the sake of the children.
"I speak to her all the time, mainly about the kids. It's important to be friends. I've told her that when you bring a child into the world it's important that child has a happy environment.
"Whatever happened between Rod and I in the past doesn't matter. How I feel reflects on my children so that's why it's important I'm happy for Rod."