Demi Lovato/Wilmer Valderrama. (WENN.COM)

Singer Demi Lovato has sparked rumours she has reignited her romance with actor Wilmer Valderrama after the former couple was spotted enjoying a dinner date together in California on Sunday.

The new X Factor judge briefly dated Valderrama last winter, but the couple broke off its relationship in January.

However, it appears they have decided to give love another go after reportedly reuniting at Lovato's 20th birthday party last month.

He also posted a telling tweet on his Twitter.com page, which read: "Feliz Cumpleaños (happy birthday) to my angel @ddlovato, U continue 2 make me proud. U are the hero this generation it's been waiting 4! With & by you always."

The reunited pair was spotted looking cozy during a meal out at Mexican restaurant El Torito in Sherman Oaks on Sunday.

Valderrama, 32, was linked to actress Minka Kelly earlier this year, while Lovato has previously dated Joe Jonas.