Demi Lovato threw Wilmer Valderrama a star-studded 35th birthday.

The 'Heart Attack' hitmaker, who has been dating the actor for four years, gathered a large group of his closest friends, including his former 'That 70s Show' co-stars Ashton Kutcher, Mila Kunis and Danny Masterson, together one day ahead of the occasion at Palm Thai restaurant in Hollywood on Thursday night (29.01.15).

Wilmer shared a picture of his birthday cake on Instagram on Friday (30.01.15), with the caption: ''IT'S MY BIRTHDAY!!!! Haha!! I was surprised last night by all the people I love!!! I felt so blessed to have looked around & truly know that everyone by my side has & will always have my back. I love you! 35, does that mean is cheaper when I go to Disneyland!? (sic)''

Ashton, who was enjoying a rare night out with fiancée Mila since welcoming their daughter, Wyatt, into the world late September, was also captured on video loudly singing 'Happy Birthday' to his close friend and after Wilmer blew out his candle, the group sang 'For He's a Jolly Good Fellow'.

Demi, 22, has been much more open about her relationship with Wilmer in recent months and recently admitted she feels like ''the luckiest girl in the world'' to be dating him.

The singer, who sought treatment in rehab for drug use, an eating disorder and self-harming disorder in 2010, also credited him for encouraging her to seek help again last year after he noticed she was showing signs of a partial relapse.

She said: ''I almost went back to rehab for my eating disorder last summer. I was obsessing over food and terrified of it at the same time. Wilmer noticed and called me out on it, which was a relief.''