Demi Lovato’s younger sister has celebrated the singer’s birthday with a moving message in which she says she is “thanking God” for the people who have supported her.

The pop star turned 26 on Monday, a month after she was taken to hospital in Los Angeles following a suspected overdose.

Her sister Madison De La Garza, 16, shared a childhood picture of the pair on Instagram, and said: “Today could have been one of the worst days of my life, but instead i get to spend it thanking God, the incredible doctors, demi’s team, and everyone across the world who offered their support – without all of these people i wouldn’t have my big sister anymore.”

today could have been one of the worst days of my life, but instead i get to spend it thanking God, the incredible doctors, demi's team, and everyone across the world who offered their support – without all of these people i wouldn't have my big sister anymore. i've been thinking about how i wish that everyone could see the silly little things that she does, like how her nostrils move when she says certain words and when she brushes my hair behind my ear when i'm trying to sleep, because those are the things i'm thankful for today. they seem so small, but those little things make up my sister – not a singer, not a celebrity, and definitely not what she's been described as in the media – she's a daughter, a friend, and my big sister… and i am so, so thankful that i can tell her happy birthday. #happybirthdaydemi ❤️

A post shared by Madison De La Garza (@maddelagarza) on Aug 20, 2018 at 10:34am PDT

The actress went on: “i’ve been thinking about how i wish that everyone could see the silly little things that she does, like how her nostrils move when she says certain words and when she brushes my hair behind my ear when i’m trying to sleep, because those are the things i’m thankful for today.

“they seem so small, but those little things make up my sister – not a singer, not a celebrity, and definitely not what she’s been described as in the media – she’s a daughter, a friend, and my big sister… and i am so, so thankful that i can tell her happy birthday. 

“#happybirthdaydemi.”

Lovato – who has been open about her battle with substance abuse – posted a message to fans earlier this month, saying she had learned addiction is “not something that disappears or fades with time” and “it is something I must continue to overcome and have not done yet”.

The star also thanked staff at the Cedars-Sinai Medical Centre in LA.

A post shared by Demi Lovato (@ddlovato) on Aug 5, 2018 at 1:53pm PDT

She added: “I now need time to heal and focus on my sobriety and road to recovery.

“The love you have all shown me will never be forgotten and I look forward to the day where I can say I came out on the other side.

“I will keep fighting.”