Demi Lovato has thanked Wilmer Valderrama for getting her through her ''darkest moments''.

The 'Skyscraper' singer posted a picture of her posing with her 'That '70s Show' actor boyfriend on his birthday yesterday (30.01.14), and thanked him for his help and support.

She wrote: ''To the funniest, most inspiring, incredible man I know.. @WilmerValderrama - thank you for helping me get through my darkest moments.. You truly are a light to this world and to my life.. Happy Birthday!!! (sic)''

Wilmer, who has just turned 34, gave an equally slushy response, writing: ''Who needs presents when the gift of you is real to us all. Thank you for the blessing of knowing you.''

The posts only further fuel speculation they are engaged, after Demi posted a picture of herself with a huge ring on her engagement finger and followed it up minutes later with a post reading: ''Sooooo I don't think I've ever been happier in my life than this very moment that I am fully living in.... (sic)''

Rumours Demi, 21, and Wilmer - who had been dating on and off since 2010 - were to get engaged were first sparked when he was seen looking for a ring at upmarket jeweller Tiffany & Co. in December, but representatives have denied the couple are set to marry.