The 25-year-old singer was taken to hospital on Tuesday (24.07.18) after suffering from an alleged heroin overdose, and although she is now awake and in a stable condition, her former partner Wilmer - whom she dated for six years before calling it quits in June 2016 - is said to be devastated by the news.
Wilmer and Demi have remained close since their split, and although the actor knew the 'Sorry Not Sorry' singer was going ''through a rough patch'', he didn't know how serious it had gotten.
A source told 'Entertainment Tonight': ''Even after they broke up, they continued to be very good friends. They have mutual admiration for each other and he has and will always believe in her. He's watched her fall and has seen her rise.
''[Wilmer] was aware she was going through a bumpy patch because she was forthright with him when she relapsed. But he did not anticipate this.''
Demi had been sober for six years before she revealed in a song entitled 'Sober' - which was released last month - that she had relapsed.
The star had previously been in rehab for her addictions, and had been vocal about her decision to get sober.
Meanwhile, it was recently reported that her apparent overdose has been a ''wake up call'' for the star, as she's now determined to get her life back on track and get sober once again.
A source said: ''Demi opened up to her friends and family that she was no longer sober, but was working on her ongoing addiction. However, Demi lost control. The overdose has been a wakeup call to Demi that she needs to get more serious about her sobriety and is telling friends and family she will do everything it takes to get back to the amazing place she was in before she slipped.''