Brooke Mueller has reportedly gone back to rehab.

The former real estate agent - who recently came to a custody arrangement with estranged husband Charlie Sheen about their two-year-old twin sons Bob and Max - is said to have entered an undisclosed facility after over the weekend after she refused a drug test on Friday, which she is required to do as part of the custody settlement.

According to gossip website TMZ, Brooke went on a drug binge last week and she decided to go into rehab before Charlie's lawyers raise the issue in court today.

Brooke - who has a history of substance abuse and had agreed to take a drug test every week until Bob and Max turn 18 - recently insisted she was a good mother and the boys were healthy and happy.

Speaking about rumours she took drugs while she was pregnant and is still addicted to illegal substances, Brooke said: "The boys are having a wonderful time. Everybody's healthy and happy.

"When people say all those mean things ... oh yeah, I think, get a life. I would say about 50 per cent of the time they're lies. The only thing I care about is that people know I'm a good mother."

Charlie and Brooke - who are in the process of finalising their divorce - reached a custody agreement last month and while Brooke will remain primary carer of the boys, Charlie will get to take them every other weekend from Saturday morning until Sunday evening for the first two months.

For the two months after that, the alternative weekend visits will be extended so Bob and Max stay in Charlie's care until Monday morning.
From then on, providing the 45-year-old star stays clean of drug and alcohol, he will be allowed to take the twins every other weekend from Saturday until Monday and also on Wednesday mornings until Thursday.

- BANG! Showbiz