Task: Question Generation
Input (English): Passage: A previously undefeated fairground boxer named "One Round" Jack Sander is beaten in the ring by a mysterious challenger, who is later revealed to be Australian Heavyweight champion Bob Corby. Bob's manager is impressed with Jack's performance and offers him the chance to become Bob's full-time sparring partner, on the condition that he win a trial fight to be arranged at a later date.
Bob begins spending more time with Jack's girlfriend Mabel and buys a bracelet for her to express his feelings. The two kiss but Mabel reluctantly puts a stop to it. The next day when Jack inquires about the bracelet Mabel lies to Jack, telling him that Bob bought it for her because he didn't want to take the money.
Jack wins his trial fight and is made Bob's official sparring partner. Keeping his earlier promise to Mabel, he agrees to marry her the next day. Mabel goes through with the wedding, although somewhat reluctantly due to her new-found feelings for Bob. At the wedding reception Bob jokingly states that he wishes Mabel had been the prize at his and Jack's original fight. Jack boldly states that he would defend his wife in a fight against any man. A friendly exhibition match is arranged between the two fighters which Bob wins. After the fight Jack sees his bride flirting with Bob and suspects that they are having an affair. Jack declares his intent to fight Bob for the heavyweight championship, but is told he is not yet ranked high enough in the league to challenge Bob. Training intensively, Jack works his way up the rankings and eventually becomes the number one contender.
Output (English): Who is the fairground boxer's sparring partner having an affair with?