It has been dismissed as one long promotional tease – but maybe Floyd Mayweather is serious about fighting Conor McGregor after all.

After many weeks of hints and intimations, Mayweather announced that he was officially coming out of retirement to take on UFC’s biggest star – and wants the much-hyped mega-fight to happen in June.

Mayweather, speaking in Liverpool on the latest leg of his UK tour, told the assembled crowd: “For Conor McGregor … I’m coming out of retirement just to fight Conor McGregor. Simple and plain, let’s fight in June.”

Mayweather’s words represent the most detailed proposal either fighter has offered for the potential showdown.

In a video posted to FightHype, Mayweather was candid about when he wanted the fight to happen. The 40-year-old said: “Everybody get your phone out. Post this to the internet as soon as possible.

“When I faced Arturo Gatti, I went to his turf. He was the A-side. I was the B-side. I beat him. I didn’t cry. I didn’t complain. When I faced Oscar De La Hoya, he was the A-side and I was the B-side. I didn’t cry. I didn’t complain. I beat him and I became the A-side.

“For Conor McGregor … I’m coming out of retirement just to fight Conor McGregor. I don’t want to hear no more excuses about the money, about the UFC. Sign the paper with the UFC so you can fight me in June. Simple and plain, let’s fight in June.”

The prospect of a Mayweather-McGregor showdown seemed a pipe dream when it was first mooted, but the talk has grown louder in recent weeks, and Mayweather told ESPN last month that a fight was “getting very, very close”.

On Saturday, Mayweather said he was tired of all the posturing and just wanted to get it done.

He taunted McGregor by saying: “You’re the B-side. I’m the A-side. We’re not here to cry about money. I’m tired of all this crying about money and saying you want to fight. You’re blowing smoke up everyone’s ass. If you want to fight, sign the paperwork.”

Mayweather retired undefeated from boxing in 2015 after beating Andre Berto. McGregor, the first fighter in the UFC’s history to hold titles in two weight divisions simultaneously, is currently on a break from MMA as he awaits the birth of his first child.

Any fight would almost certainly be under boxing rules. McGregor has already taken steps to make sure he’s able to fight in Las Vegas by obtaining a boxing license from the Nevada State Athletic Commission.

But the sticking point still looks certain to be money. McGregor has said he wants $100m for the fight – a similar amount to the sum Mayweather made when he fought Manny Pacquiao in May 2015. So far, the only concrete offer has come from UFC president Dana White, who offered both men $25m.

In retort, Mayweather described White as a “fucking comedian”.