Charlie McDowell has hit back at social media users who posted "unkind messages about surrogacy".

The 41-year-old screenwriter and Lily Collins, his wife, recently announced that they've welcomed a baby girl via a surrogate, and Charlie has now taken to Instagram to defend their decision.

He wrote on the photo-sharing platform: "Thank you for all the kind messages and love. We are overjoyed and very grateful. In regards to the unkind messages about surrogacy and our path to having a baby - it's OK to not be an expert on surrogacy.

"It's OK to not know why someone might need a surrogate to have a child. It's OK to not know the motivations of a surrogate regardless of what you assume. And it's OK to spend less time spewing hateful words into the world, especially in regards to a beautiful baby girl who has brought a lot of love into people's lives. That's all for now because she just pooped and I need to change her diaper. (sic)"

Prior to that, Lily and Charlie announced the arrival of their baby girl.

The 35-year-old actress actually shared a photograph of their daughter on Instagram.

She captioned the snap: "Welcome to the center of our world Tove Jane McDowell. Words will never express our endless gratitude for our incredible surrogate and everyone who helped us along the way. We love you to the moon and back again… (sic)"

Lily previously revealed that she was keen to have children.

The actress - who battled an eating disorder during her teenage years - actually decided to discuss her health troubles publicly because she had a long-term ambition of starting a family.

Speaking to Us Weekly back in 2017, Lily explained: "Everyone has a different form of recovery. I never had an 'aha' moment.

"My reason to finally start talking about [my eating disorder] was the moment I realized I wanted a family. I wanted kids. I didn't want this to be something I bring into that."