Former unified heavyweight world titlist Anthony Joshua, who suffered one of the biggest upset losses in boxing history on Saturday night at Madison Square Garden in New York, said during his postfight interview in the ring that he intended to exercise his contractual right to an immediate rematch.

Joshua did just that on Tuesday, assuring that there will be a sequel with Andy Ruiz Jr. later this year. Eddie Hearn of Matchroom Boxing, Joshua's promoter, announced the development on social media after meeting with Joshua and his trainer/adviser Robert McCracken.

"After meetings with AJ, Rob Mc and the management team in NY, we have today triggered the contracted rematch clause with Andy Ruiz Jnr. The fight will take place in Nov/Dec at a venue to be confirmed shortly," Hearn wrote.

Joshua had 30 days to decide whether he wanted to exercise his right to the rematch but took no time at all, immediately electing to seek revenge for his seventh-round knockout loss, one of the most shocking results in boxing history.

"There was no point in waiting," Hearn told ESPN. "We've talked about it and it's happening. There's no other fight AJ wants, so there was no point waiting 30 days. Everybody needs clarity. We sat down and it wasn't even a case of him asking what else is out there. The rematch is the fight we need, and that's what we'll be doing."

As for the date and location, Hearn told ESPN that November was more likely than December and "my gut feeling was the U.K. but not guaranteed. We have to look at everything. The people at DAZN [the U.S. broadcaster] and Madison Square Garden would like to do Part 2 in the U.S. Joshua came to Andy Ruiz's country for the first fight, so it kind of makes sense to the second fight in the U.K. So we'll see."

Joshua (22-1, 21 KOs), 29, a huge star in the United Kingdom, was making his United States debut against replacement opponent Ruiz on Saturday night looking to retain his title for the seventh time and make a splash on these shores. He looked like he might take the heavy underdog Ruiz out early when he knocked him down with a left hook in the dramatic third round. But Ruiz shook off the knockdown and rebounded to knock Joshua down twice later in the round.

Joshua never really recovered, and in the seventh round, Ruiz dropped him twice more before referee Michael Griffin waved off the fight, with a seemingly spent Joshua leaning against one of the corner posts with his arms resting on the top ropes.

"It's an upset. One shot on top of the dome rattled me quite a bit. Tried to stay in there a few more rounds but the better man won. Respect to Andy and I move forward and look out for the end of the year," said Joshua, more than two hours after the fight, when he decided to meet the few remaining media members still at the Garden after it had been announced he would not appear because of a concussion. "I never underestimate anyone. He's a decent puncher, decent fighter. This was his chance, and I always say anyone who comes to box me is 50, 20 percent better than what we've seen. These guys are coming to win and he was the better man."

Joshua gave Ruiz credit for his victory but said he was eager to fight him again.

"It's a minor setback, if that's what you want to call it. I feel like this is just part of the journey I'm on, and this is boxing, so what I have to do is evaluate the situation, make it better and we go again," Joshua said. "I just got beat tonight. On the record it says I got beat, and that's it. It's a test of character. I don't want to say this went wrong, that went wrong. I ain't dwelling on this. Just move forward, correct it.

"I'll bounce back and get my hands on those belts again. ... I'm gonna beat him up. Tidy up, brush off the cobwebs and fight again. Losing is something we can learn from. Tighten up. Get smart. There's more to come. Winning is everything, but if you do happen to take an 'L,' reset, readjust and bounce back. I do not condone losing. On to the next one. The hunger is always there. I'm ready to go back to work tomorrow."

Ruiz's victory made him the first boxer of Mexican descent to win a heavyweight world title. He had replaced Jarrell "Big Baby" Miller on about four weeks' notice after Miller was dropped from the bout because of four positive drug tests for a variety of banned substances.

During his postfight news conference, Ruiz (33-1, 22 KOs), 29, the son of Mexican immigrants from Imperial, California, said he will enjoy his upset victory and the celebration to come -- he will appear Tuesday night on Jimmy Kimmel's late-night talk show and his team is sorting through numerous other appearance offers -- but that he will ready for the rematch. He earned more than $3 million for Saturday night's fight, and his purse for the rematch will be more than double that.

Ruiz said nobody should have underestimated him in the first place despite his rotund body type and 4-inch height disadvantage against the 6-foot-6 Joshua.

"The way I look, the extra flab that I carry -- now I want to get in really good shape and look like a Mexican Anthony next time we fight," Ruiz said with a laugh about why he was so dismissed. "We made it happen. No one can take that from me. Nobody. I just shocked the world. Now I've got to work even harder and make a legacy. I'm not going to let these belts go."