Alexander Zverev explains the eye-catching routine he and his glamorous partner perform before their matches after being caught on camera at the Australian Open.

Alexander Zverev has coyly explained the secret handshake he has been sharing with partner Sophia Thomalla at the Australian Open after it caught the attention of tennis fans.

Second seed Zverev, chasing an elusive first Grand Slam title, beat Tommy Paul 7-6 (7-1) 7-6 (7-0) 2-6 6-1 on Tuesday during their quarterfinal of Grand Slam.

Zverev was later questioned by tennis great-turned-commentator Jim Courier about a ritual handshake he was caught doing with his girlfriend in the players' area before matches.

Courier embarrassed the tennis star by playing the clip to the delighted crowd at Rod Laver Arena.

'What are you doing to me? I only played four hours… I mean, we've been together for three and a half years now,” the 27-year-old smiled.

'Look, man, you have to understand that we are German, this is the best version of German you can be.

Alexander Zverev was questioned about the secret handshake he was caught having with his partner Sophia Thomalla before their matches at the Australian Open.

“This is the peak of German coldness, it goes no further. We did it, we did it well.”

Courier responded: “I've been married for 14 years, my wife and I don't hold hands, we have to go.”

He will next face ten-time champion Novak Djokovic in his third semi-final at Melbourne Park.

Zverev, tennis's biggest unsatisfied talent, with two Grand Slam final losses to his name, won the first set in a tiebreaker, fighting back after Paul served for the set at 6-5.

But with Paul on serve leading the second set 4-2, Zverev bristled.

The German got angry with the chair umpire when he had to retake a point because a feather fell near the ball just as he was about to hit it.

The 27-year-old dropped the next point and received a code violation for yelling the F-bomb.

The German player and his girlfriend Sophia Thomalla (in the photo) have been together for three and a half years

Thomalla is a model, actress and television presenter who has also starred in several television dramas in Germany.

Then, at number two, a point was replayed after a feather fell near the ball just as Zverev was about to hit it, and Paul received another first serve.

Zverev ripped the feather, courtesy of one of the many seagulls in the rafters of Rod Laver Arena, off the court and swung it at the referee in frustration.

'Dude, it's a feather!' Zverev said.

“There are millions of them on the court.”

But rather than implode, the German showed he was no featherweight, appearing unflappable as he forced the set to a tiebreaker.

“I've never had that thing about stopping a point because of a feather before. So that was new for me,” Zverev laughed after the match.

Zverev will face Novak Djokovic in their third semi-final at Melbourne Park

I'm not sure it was a hindrance to anyone. It's not like a hard object. Even if the tennis ball hits the pen, it doesn't really change anything.

'It doesn't change the trajectory of the ball or the bounce of the ball or anything like that.

'But yeah, I don't know. Maybe the referee made the right decision and maybe not. I have no idea.

“But it was a little frustrating because obviously Tommy would get a first serve and he won the point on that serve as well.”

'I got a warning after that. So a lot of things happened at that time.”