They may be best friends, but Sienna Miller is apparently not going to be giving any parenting advice to Keira Knightley: because she thinks she’ll be “perfect” as a mother.

Speaking to the New York Post’s ‘Page Six’ section, the 32 year old actress and star of recent film American Sniper said that Knightley will be an “amazing” mother and doesn’t need any help. “We’ve spoken a lot and I know she will be amazing,” Miller said. “She doesn’t need any advice. She will be perfect.”

Sienna Miller
Sienna Miller, picture above with her daughter Marlowe, reckons Keira Knightley will be a "perfect" mother

29 year old Knightley revealed last week that she and her husband James Righton, a former member of the recently demised British nu-rave group Klaxons, were expecting their first child together.

More: Keira Knightley confirms she is pregnant with her first child

Miller recently posed with her own two year old daughter Marlowe in Vogue magazine (January edition), and she revealed that when she became a mother back in July 2012 she was struck by how natural it felt for her.

“I was overwhelmed by how normal it felt. It was like, 'There you are - that's what I have been missing.' Like we're both in on something only we know. An amazing sense of being complicit with a little being.”

She has been in a relationship with her current boyfriend Tom Sturridge (29) for over three years and is enjoying the stability that her life provides. "Tom is a grounded, intelligent, kind, and intact person. That's amazing to be around. That's the father of my child. There's no drama."

Miller and Knightley have remained good friends since they worked together back in 2008 on the Dylan Thomas biopic The Edge of Love.

More: Watch Bradley Cooper in the trailer for American Sniper