Denise Richards has joked she adopted because Charlie Sheen was "a little too tied up" to have more kids.

The American star and her ex-husband Charlie have two daughters together, Sam, seven, and six-year-old Lola. Denise adopted a baby girl called Eloise earlier this year, and has discussed why she wanted to become a mother again.

Charlie's had a turbulent time in 2011, going to rehab and getting sacked from Two and a Half Men. He is now back on track and is pleased Denise is a mother again.

"I could have either wait until I have the right partner or just [become a mom] on my own and I decided to do it on my own. It was about a two-year process and she's an amazing blessing. She's almost five months this week," Denise told talk show host Chelsea Lately.

When Chelsea sarcastically asked why Denise hadn't decided to have more children with Charlie, the star replied: "He's a little tied up."

The pair went on to talk about how Denise copes with being Charlie's ex-wife. He famously had a meltdown while on holiday with Denise and their kids last year, resulting in him being hospitalised after trashing his hotel room.

The 40-year-old actress explained the key has been realising her ex-husband will never change.

"Well there's times I don't bite my tongue, but keep it about the kids and I think it's important for them to see us get along," she explained. "I've learnt to accept him for who he is, I can't change him. I've said this before, when he's off doing his thing then obviously he doesn't see the girls. When he's straight and good then obviously they spend time with him."