The former couple dated for four years before splitting in 2015 and they now co-parent their nine-year-old daughter, Marlowe.
Over the weekend, the duo were spotted on a double date at Wimbledon — where they each brought along their new significant others.
Not only that, but the outing also marked Tom's first public appearance with his girlfriend, model Alexa Chung.
Meanwhile, Sienna was joined by her boyfriend, Oli Green, whom she's been linked to since February of this year.
The two couples didn't hold back on their personal PDA — and later even snapped some selfies together.
While the whole thing might have been completely awkward for most people, the group actually seemed to really enjoy the afternoon.
And that makes sense, considering Sienna has said that the exes are on really good terms — and actually lived together at one point.
"Everybody will stay over or we'll all go on holiday and that's because we genuinely want to be around each other," she once told Harper's Bazaar, adding, "It's great for our daughter that she has two parents who love each other and are friends. He's definitely my best friend in the entire world."
It's nice to see that Tom and Sienna have been able to stay so close over the years!