Wilmer Valderrama sent Demi Lovato a romantic birthday message on Instagram yesterday (20.08.14).

The 34-year-old actor, who likes to keep his relationship private, took to the social networking site in a rare show of affection to mark the 'Heart Attack' hitmaker's 22nd milestone and declare his love for her.

Wilmer posted an adorable photograph of him and Demi laughing together, along with the caption: ''Wishing you happy birthday would never come close to all the inspiring things I wish for your life.. We laugh our asses off.. While we do all we can do better everything around us... Love you through all. (sic).''

The hunk's heartfelt message comes just eight months after Demi posted a similar post on her Instagram account to celebrate his birthday in January.

She wrote alongside a picture of them together: ''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)''

Meanwhile, the couple - who have been dating on/off since 2010 - sparked rumours they had got engaged in December after Wilmer was spotted buying a ring from Tiffany & Co., which he had engraved with a special message reading, ''With you and by you always.''