The pair were spotted at the singer's Camden home at 1.30am yesterday. Horgan-Wallace left the flat four hours later wearing a pair of Winehouse's shoes.
Winehouse's list of celebrity friends includes Kelly Osbourne, Kimberley Stewart, Miquita Oliver, Pete Doherty and Alan Carr.
The troubled star is currently working on the follow-up to her 2006 album Back To Black.
It was reported earlier this week that Winehouse's new LP was sounding dark and "suicidal" because of her recent reclusive behaviour.