The Burn hitmaker played an acoustic headline set at the Shepherd's Bush Empire venue to raise money for the Streets of London homeless charity.
The MCBusted star, who has been dating Goulding since earlier this year (14), joined her onstage to play the tambourine.
Goulding posted a picture of Instagram.com of the couple giggling and hugging each other as he arrived on stage.
The surprise appearance comes just days after Goulding joined MCBusted for a performance on The X Factor's sister show The Xtra Factor over the weekend (13-14Dec14). She played electric guitar with the group as they sang new single Air Guitar.