The walking boot that Sen. John McCain has worn since receiving treatment for a recent injury appears to have swapped feet.

The Arizona Republican tweeted on Wednesday a photo of himself sitting next to his wife, Cindy McCain, attending their daughter's wedding at their ranch in Arizona.

The boot, which McCain has worn since his treatment for a minor tear in his right Achilles tendon at the beginning of the month, has appeared on his right foot in a number of photos the senator has shared on Twitter in the last couple weeks.

But Twitter users Wednesday noted that the boot in the latest photo appeared to be on his left foot. It was unclear whether the photo McCain shared was mirrored for some reason, but it did prompt a fierce debate and conspiracy theories on social media.

On Thursday, Thanksgiving, McCain tweeted an explanation for the swap, saying that his left leg had been "doing extra work to compensate for the boot" so he had been "giving it a break."

McCain, who is 81 years old, was also diagnosed with stage four glioblastoma, an aggressive form of brain cancer, over the summer. He has since returned to Washington, D.C., for work following the first round of chemotherapy and radiation.