Richard Branson made a bet with a rival CEO that involves 'a knee in the groin' - and he's ready to collect

"If Willie is planning to have any more kids, he had better get a move on!" Virgin Group founder Sir Richard Branson wrote in his new autobiography titled "Finding My Virginity."

The "Willie" in question is International Airlines Group CEO Willie Walsh. Branson is concerned about his ability to reproduce because of a bet the two made years ago.

Shortly after Delta acquired 49% of Virgin Atlantic Airways in 2012, Walsh predicted that the Virgin Atlantic would not exist in five years' time.

"I can't see Delta wanting to operate the Virgin Brand, because if they do, what does that say about the Delta brand?" Walsh said at the time.

Walsh's IAG owns rival British Airways and Iberia among other airlines.

"Willie's claim was absolute rubbish - I had no intention of letting Virgin Atlantic Disappear, and neither did Delta," Branson wrote in his book. "While I usually laugh off criticism, when I see our competitors overstepping the line, I will protect my teams in every way I can."

In response, Branson challenged Walsh to a bet: "If Virgin Atlantic was still flying in five years time, [British Airways] had to give £1 million ($1.31 million) to our staff."

If Virgin Atlantic was no longer flying, Branson promised to personally pay BA employees £1 million of his own money.

However, Walsh wasn't quite impressed by the offer.

"Branson is a billionaire banker, allegedly. I'm not a billionaire. So maybe a bet that would have as much pain to me as it would to him - a knee in the groin," the IAG CEO said in response at a press conference.

Branson gladly accepted.

"It seems a very painful and foolish thing for Willie Walsh to propose," he wrote on his blog at the time. "But I would be happy to accept."

Which brings us back to today. That five years period ends in December.

It seems Branson is keen on collecting on the bet.

In fact, this is the second time in recent months Branson has publicly reminded Walsh of the wager.

"Willie Walsh predicted that the Virgin Atlantic brand would disappear within five years as a result," Branson wrote on his blog in July. "Whether childishly or bravely, he also said he'd accept a knee in the groin from me if it didn't. Well, Willie, that five-year point is up this December. And Virgin Atlantic is still flying strong!"