They're both in New York starring in Broadway plays, so it's not so surprising that these two would be bumping into each other and probably even less surprising that they'd be bumping uglies!

"Sienna and Jude have met up a few times and got on really well," says a source. But the most "Awwwww" inducing part of this story, reported by Now, is that Sienna's dog Bess, whom we've caught her out walking several times in New York, is what brought the exes back together.

"Sienna invited him to Bess's birthday party," the source continues, "which was poignant considering that Jude bought Bess, and her other dog Porgy, as a gift."

The exes are currently working only one block away from each other, and apparently are using Jude's best pal (and Sienna's co-star) Jonny Lee Miller as a beard.

"Jonny's great at throwing the paparazzi off the scent," a spy told the mag. "He'll walk down the street with Sienna to where Jude's staying just round the corner." Sooo sneaky!

Sienna and Jude first broke up in 2006, after she caught him cheating with the nanny, but has always admitted that she's kept a special place in her heart for Jude.

Now that they're both in New York, and both single, the timing couldn't be better! Even if he did just have a kid, who cares? It's not like he's even seen her yet!