A French Open ball girl has revealed Roger Federer’s extraordinary act of kindness during one of the toughest moments of his career.

Federer endured a lean year by his standards in 2011 and did not hold any of the four major titles for the first time since 2003.

But a stunning defeat of Novak Djokovic in the French Open semis — which ended a 43-match winning streak the Serb was riding — gave him a chance of a second Roland Garros title.

But it wasn’t to be as French master Rafael Nadal enjoyed the better of three incredibly tight sets before winning 7–5 7–6 5–7 6–1.

Kenza Del was on ball kid duties in the match and during a touching moment was captured scrawling the words “Allez Roger” [Go Roger] in the clay in a show of support.

The moment went viral.

Ahead of this year’s tournament, which begins next month, Del has explained her motivation for breaking Roland Garros’ rules — and how she was rewarded by the Swiss champion.

“It was a tough moment for him. And I don’t know why but I decided to write Allez Roger,” she said.

A picture of the moment found its way to Federer and he decided to thank her by sending Del a personal gift.

He sent her a frame with the iconic red shirt that he wore during the match, along with an autograph.

The moment clearly still has a special place in Federer’s heart.

When Kenza’s story was posted on Instagram this week, Federer commented, “Merci Kenza [Thank you Kenza]”.

Del said she wanted to thank the photographer for helping her connect with the legend.

“I never got to meet the photographer, never got the chance to thank him.

“So, if he watches this video, if he hears me, I’ll be glad to thank him, because it’s all thanks to him.”

And the story is still making waves. Tennis writer Bastien Fachan wrote: “I’d never heard about this story, wow.”