They were Best Friends for twelve years.
Only a year apart, they were inseparable. Where you saw Opie, Jack was nearby. They literally slept wrapped around each other for most of their lives, especially during their golden years.
Sadly we lost Jack last year to cancer. He was a special boy having been born under a neighbor's deck to Peaches. Jesse was Jack's littermate but because Jesse remained a garage cat (due to unprovoked spraying), the brothers didn't see each other for many years.