Demi Lovato Dating Wilmer Valderrama? 'That 70s Show' Star Wishes 'Heart Attack' Songstress Sweet, Affectionate Happy Birthday on Twitter, Romance Rumors Rekindled

"Heart Attack" songstress Demi Lovato just turned 21 on August 20, and "ex-boyfriend" Wilmer Valderrama sent the "X-Factor" beauty a loving shout-out on Twitter in celebration of such a monumental age. The tweet is rather sweet and affectionate... does this mean Lovato and the former "That 70s Show" funny-man are secretly dating?

On Tuesday, Valderrama tweeted:

@WValderrama: "I've been so proud of the strength & commitment you've gained 4 life, keep inspiring us all! Happy birthday my @ddlovato! With & by u always."

Lovato and the 33-year-old "Yo Momma" actor never came out as an official "couple," but rumors suggest they were romantically involved a couple of years ago. And this past Valentine's Day, the duo shared a romantic dinner in LA.

"They ordered almost everything on the menu, but they didn't touch it for at least an hour. They stared into each other's eyes the whole time," an eyewitness told US Weekly at the time.

Following the death of Lovato's father Patrick back in June, Valderrama has continued to offer his full love and support:

"[Wilmer] is her rock and he has been in constant contact with her, both by text and in person, during this difficult time and he'll continue to be her shoulder to cry on," an insider tells Hollywood Life.

How sweet! Do Mstars fans think they'd make a cute couple?