East Rutherford, New Jersey - When Lionel Messi and Lamine Yamal line up against each other in the World Cup final on Sunday, it will mark the closing of an incredible full-circle moment that has been two decades in the making.

In 2007, a 20-year-old Messi and Yamal, born in July of that year, posed together in a photo organised by UNICEF, the global agency that provides humanitarian and development assistance to children and mothers worldwide.

Yamal's family had entered and won a raffle to pose with a Barcelona player for a 2008 UNICEF calendar.

In one photo from the shoot, Messi is seen helping Yamal's mother, Sheila Ebana, give the smiling five-month-old boy a bath in a blue plastic tub.

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"The photographer, Joan Monfort, has said that Lamine Yamal stole Messi's heart because he was always smiling," UNICEF Catalan's Laia Ruich said on the organisation's website.

Fast forward nearly 20 years, and now Messi and Yamal are sharing soccer's greatest stage.

Spain star Yamal, the teenage prodigy who has followed in Messi's footsteps at Barcelona, has only just turned 19.

Argentina captain Messi (39) will be playing in his third World Cup final in what is almost certainly likely to be his last appearance in the tournament.

"That photo is incredible," Messi said at a fan event in Manhattan on Friday.

"I took a picture with him when he was a baby... the fact that we're both playing in the World Cup now is crazy."

Messi said while he has a soft spot for Yamal given his association with his former club Barcelona, it will not detract him from the task in hand on Sunday – beating Spain.

"I wish him luck because his success will be Barcelona's success, [but] we'll try to keep him from playing at his best.

"He's 19 years old and has his whole career ahead of him. I wish him the best, but we'll give it our all to ensure he doesn't become champion this time."

Photographer Monfort describes Messi and Yamal's first meeting and subsequent World Cup final date as "a true miracle of destiny."

"If you wrote this in a film, it would not seem possible," Monfort told the BBC.

Even Yamal's Spain teammate, Mikel Merino, said Friday he initially believed the photo was an AI-generated hoax when he first saw it.

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"The first time I saw it, I thought it was AI and that it wasn't even real," Merino said.

"It's unbelievable that two of the best players to have played the game – and hopefully Lamine, in the future, will be one of those – share a picture like that."

Messi and Yamal now both serve as UNICEF Goodwill Ambassadors.

"Growing up, all I had was a family, a ball, a park and a dream," Yamal said in June.

"Playing football gave me structure, a sense of belonging, and hope for the future.

"I know how important it is for children to have a safe place to play, so that they can simply enjoy being children."