His MMA career is over. This is what UFC heavyweight champion and professional wrestling star Brock Lesnar implied with his new contract with the WWE.

On Tuesday, the 37-year-old fighter said he already re-signed with the WWE which ended speculations that he will be returning to the Octagon, ESPN reported.

"I'm officially closing the door on MMA. It was hard. I re-signed last night with the WWE," he was quoted by ESPN as saying.

Lesnar will fight against Roman Reigns at Wrestlemania 31 this weekend in Santa Clara, California. His current contract with the WWE will reportedly expire by the end of the month so people thought that he will already return to the MMA.

"It was a very hard decision at this stage of my career. The fighter inside me wants to compete. The father and husband -- I'm an older caveman now. I make wiser caveman decisions. So, I'm here to say my legacy in the Octagon is over," he added.

Lesnar also discussed that it took him a year to come up with this decision but he noted that he wanted to "have fun."

"The last two-and-a-half months I've been training to get back into the Octagon. I felt physically great, but something lacked mentally -- and that's not good," he was quoted by ESPN as saying.

The WWE champion was seen on the cageside at a UFC event in Los Angeles where Ronda Rousey fought.

A Bleacher Report article discussed that Lesnar's rumored return to the Octagon had something to do with "the regret of having unfinished business in the sport after walking away due to diverticulitis in 2011."

During his last appearance at UFC 141 against Alistair Overeem, ESPN said Lesnar expressed his concerns in going back to the MMA.

"I could go back to the Octagon, but what am I going to gain? I was the UFC heavyweight champion of the world. Due to my illness, my career got cut short. That's God telling you, 'it's time to move on,'" he added.

His retirement from the support did not prove to be bad for Lesnar as it paved the way for him to join WWE and become one of its leading stars.

According to Bleacher Report, his "mainstream appeal and imposing force" became his tools to be part of Reality Era, which helped WWE gain coverage even from outlets "not typically predisposed to covering its programming."

In August last year, Lesnar became the champion when he defeated John Cena at SummerSlam and was able to keep his belt even in WrestleMania against Reigns.

On Sunday, he is set to defend his title again on Sunday against Reigns at WrestleMania 31 which will take place at the Levi's® Stadium. Tickets range from $35 to $1,000 per ticket.