The 28-year-old singer shared a loved-up message on her Instagram Story as she described Max - who she got engaged to in May after meeting in March - as ''the best father'' to their pet dogs.
She said: ''Happy six months to my darling, the best father these pups could ever ask for.
''I love you beyond. Thank you for making my life so much better @maxehrich. I love you, baby! (sic)''
Demi's sweet words come after she revealed she ''fell in love'' with Max after meeting six months ago and enjoying a ''whirlwind romance''.
She recently explained: ''I met my fiance in March and I fell in love with him. We've had this whirlwind romance and have been able to spend this time together.
''I knew that I wanted to learn something from this time that could actually better my life, my mental health and my emotional wellbeing in the long term.
''Initially I was resistant, but because my fiance is so positive all the time, I just started picking up on the things he does.
''I started meditating and doing yoga. I started journaling, painting, taking pictures and being creative, and learning to appreciate nature, after realising I'd been taking it for granted all this time.''
Meanwhile, Demi previously admitted that their romance was a case of love at first sight.
She wrote on Twitter in July: ''When I was a little girl, my birth dad always called me his ''little partner'' - something that might've sounded strange without his southern cowboy like accent.
''To me it made perfect sense. And today that word makes perfect sense again but today I'm officially going to be someone else's partner.
''@maxehrich - I knew I loved you the moment I met you. It was something I can't describe to anyone who hasn't experienced it firsthand but luckily you did too.. I've never felt so unconditionally loved by someone in my life (other than my parents) flaws and all (sic)''
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