Britney cut short a night of partying and rushed to his rented flat, where she stayed until 4am.
A source said: "Justin had been planning to meet record execs in Manhattan for a while."
"But when when he spoke to Britney it seemed like a good idea to fly straight over. She seemed fairly chirpy about her split from Isaac but Justin was worried about her and about her partying too much.
"He thought it would be nice for them to hang out and see some sights. Justin reckons he can keep Britney away from the clubs."
The source continued: "Britney was on good form but she was starting to attract the wrong kind of attention in the club. A complete stranger grabbed her thong. She seemed really pleased to hear from Justin and couldn’t wait to see him."
"He’s renting a flat in Greenwich and they holed up there for quite a while. Britney eventually left at 4.20 in the morning with a big grin on her face."
"They’re both free and single now so who knows what they were getting up to. Whatever there is between those two old friends is still burning strong."
Like the source says, they are both single now...