She was recently admitted to rehab, apparently still struggling to come to terms with the end of their relationship.
Judging by Borrell's perfomance last night, Watson could have her hands full with the hell-raising rock star.
Emma and Johnny turned out at the Vanity Fair party along with a host of stars, including Lily Allen, Pixie Geldof, Twiggy, Bryan Ferry and Will Young to celebrate the launch of an exhibition of photographic portraits which have appeared in the US magazine Vanity Fair over the course of nearly 100 years.
Borrell's ex-girlfriend Camilla Fayed was also at the event.
Pixie Geldof, 17, the daughter of Bob Geldof, mixed with singer and chat show host Lily Allen, 22, and daughter of actor and hardman Keith Allen, who in turn chatted with Kate Sumner, 25, the daughter of Sting.