'The Three Amigos' John McCain, Lindsey Graham, Joe Lieberman go hiking in Arizona (ABC News)

The boys are back.

Sen. John McCain, R-Ariz., Sen. Lindsey Graham, R-S.C., and former Sen. Joe Lieberman, I-Conn. -- previously dubbed "The Three Amigos" by retired general David Petraeus -- headed on Saturday to Arizona's Oak Creek Canyon, where they went hiking and waded in water. McCain's daughter Meghan joined the trio.

"The three amigos together again!" tweeted McCain, along with a photo of the casually-dressed, baseball cap-wearing group.

McCain, who is battling brain cancer, has finished his first round of chemotherapy and radiation treatment, Meghan announced on Friday.

The three amigos together again! pic.twitter.com/IciasfFaPJ — John McCain (@SenJohnMcCain) August 19, 2017

In another photo McCain tweeted, he and Lieberman are wading in the water. "Where's Lindsey?" McCain wrote, illustrating his sense of humor.

In a photo posted on Instagram which includes Meghan with her dad and his friends, Meghan wrote, "Morning hike with The Three Amigos! @senjohnmccain @lindseygrahamsc Joe Lieberman!"