The two couldn't stop chatting and laughing as they realised they were sat near each other, with Pippa's younger brother James also getting in on the action and Michelle introducing boyfriend John Dineen.
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Pippa and James Middleton catch up with Michelle Dockery
Wearing a floral black-and-white summer dress, stylish Pippa was Wimbledon-ready and added a smart tailored blazer to the outfit to keep off any chill as she watched Thursday's Lukas Rosol v Rafael Nadal match.
Michelle and boyfriend John both wore navy blue jackets while Michelle teamed her cover-up with a sleeveless black shift dress.
The friends first met several years ago when Pippa and James visited the set of the hit ITV drama.
Fans of the show, Michelle had previously told Vanity Fair magazine of meeting the two.
Pippa Middleton at Wimbledon 2014
"They are friends of Alastair Bruce who is our historical adviser and the royal correspondent [for Sky News], so he's had a lot of involvement with the royal family. That’s why they came. And it was shortly after the [royal] wedding. It was amazing talking to them. And I hear that Will and Kate are fans, too, which is great", Michelle told the magazine.
Cycling as part of an eight-person group, the teams cycled through 12 states in six days, ten hours and 54 minutes in order to raise money for the British Heart Foundation and the Michael Matthews Foundation.
Pippa Middleton and Michelle Dockery at Wimbledon 2014
James and Pippa's trip attracted much attention Stateside and fans spotted them taking a pit stop in rural Missouri on Wednesday.
Four days into the ride the group stopped off to refuel at a McDonald's restaurant where local residents snapped them tucking into some food.
Pippa, 30, and James, 27, then both posed for photographs before loading up their bikes and jumping into a waiting black vehicle, presumably headed for a nearby hotel to get some rest.