“I answer it and I see my brother, and in the back you could see almost the whole team,” Frank Theis said in a telephone interview. “Like, Kyrie [Irving] was there. And I’m sitting there like, ‘Oh, my! There’s Kyrie!’ ”

LONDON — After a game at the start of this season, Celtics rookie Daniel Theis made a FaceTime video call to his older brother Frank back in Germany. He wanted to show him his new, splashy, green-tinted workspace.

Frank Theis was so star-struck that he grabbed another phone and made a video call to a friend so he could see Irving and the Celtics, too. That was the moment it hit him that his younger brother had truly made it. Daniel was living out a dream for both of them.


On Thursday, Frank Theis will make the one-hour flight from his home in Braunschweig, Germany, to London to see the Celtics play the 76ers. It will be the first time he sees his brother play in an NBA game. When he thinks about that moment, he said, he shakes with excitement and cannot sleep.

The NBA organizes these international games to expand its global footprint. But for players such as Theis and Celtics rookie Guerschon Yabusele, who is from France, this game offers a rare chance to perform closer to home.

“It means a lot, especially to have my brother there,” Theis said. “I know he is excited, too.”

That might be an understatement.

“This is absolutely crazy for me,” Frank Theis said. “Yeah, I’m 10 years older than him, but in my youth, I was a freaking NBA fan and this was a dream for me, and now my brother is there and I can watch him play. This is absolutely crazy.”


When Frank Theis was growing up in Salzgitter, a small city in central Germany, his bedroom was decorated with Chicago Bulls posters and pictures. He wanted to be like Michael Jordan. He did not do that, but he did become a powerful 6-foot-7-inch forward.

Soccer was Daniel’s initial love, but his family tried to sway him. His father said that if he switched to basketball, he would buy him sneakers, jerseys, and shorts — whatever he wanted. The father reasoned that soccer was too slow and boring, and that the fast-paced nature of basketball better suited him.

Daniel somewhat reluctantly transitioned, but mostly because he wanted to be like his older brother. When Daniel was 7 and Frank was 17, Daniel always tried to find his way onto the court with his brother.

“I told him every time he knocked on my room, ‘Danny, please go away. You have no chance,’ ” Frank Theis recalled with a chuckle. “Then he’d come in my room and play PlayStation.”

Teaming up

Frank Theis began playing for a German second-division pro team, the Wolfenbuttel Dukes, when he was 20 years old. Young Daniel was rapt.

He would go to practices and wait for any free moment to fire up jump shots. He would sit courtside at home games and film the action with a camcorder, perhaps the youngest video coordinator in basketball. He would even go on six-hour bus rides for road games when his school schedule allowed.

“Everybody would tell him he should be with his friends, and he would say, ‘No, I will go with my brother,’ ” Frank said. “This was his start. Then he started playing basketball every day.”


Theis eventually blossomed into an athletic 6-9 forward with impossibly long arms and a soft shooting touch. His only real flaw was his ball-handling, and his older brother would jokingly remind him of that often.

Daniel was just 18 in 2010 when he joined the second-division team in Braunschweig, and he and Frank were teammates for two seasons. Daniel then progressed to the first division while knee injuries and age ended Frank’s career.

What a pic! On court with my big brother Frank Theis and my 🏀-brother @DennisMike93 😎👊🏼🔥 #5YearsAgo #Throwback pic.twitter.com/T6ciHSCsFG — Daniel Theis (@dtheis10) September 16, 2017

As Daniel developed into a defensive force, the NBA became a more realistic goal. But he had a pair of failed tryouts, including a 2014 summer-league stint with the Washington Wizards.

“He came back and said it was not good,” Frank Theis said. “He said he had a big chance but can’t do it. And I told him maybe it’s time to cut this story, and maybe you try your best in Europe.”

But last year Theis was named the Defensive Player of the Year in the top-level German Bundesliga, and in the spring, a new hope emerged. The Celtics had been watching Theis for years, and they knew if they signed Gordon Hayward they would need to renounce their rights to all of their free-agent big men, making a minimum-salary player like Theis quite attractive.

Theis, who was playing and living in Bamberg, called Frank and told him that Boston had expressed real interest, and that talks were intensifying. Frank was so excited that he could not sleep that night. The next morning he drove about 250 miles from Braunschweig to Bamberg. He stayed with his brother for two days, and then Daniel agreed to sign with Boston.


“I’m freaking out and I’m yelling, and my brother is so calm, like, ‘It’s cool,’ ” Frank said. “The NBA was so far away in my youth. My whole room was pictures and posters, and now my brother is there.

“For my brother, maybe it’s a little bit normal. But for me it is just, wow.”

The Theis family had a celebratory barbecue and partied deep into the night. Daniel was really headed to the NBA, really headed to Boston.

Nothing will spoil this

This season, Daniel has established an important role for himself as a backup center. He is averaging 4.7 points and 4.2 rebounds in just 13.2 minutes per game and has had shining moments defensively.

Frank live-streams games as often as possible, but he is a middle school teacher now, and the Celtics’ frequent 1:30 a.m. tipoffs sometimes cause him to wait until the afternoon. His students are aware of his famous brother, and many are NBA fans, too. So when Frank misses a game that he intends to watch later, he pleads with his students not to spoil it.

“Sometimes students come in my class and tell me, ‘You are Daniel’s brother?’ ” Frank said. “I say yes, and they say it’s so cool. This is crazy. Sometimes I couldn’t realize how crazy it is. But when students come to me, it hits me. Yes, it is Daniel, and he is in the NBA.”


Daniel Theis has found a niche with the Celtics. matthew j. lee/globe staff

The Theis brothers’ parents usually watch highlights the next day. Their father is retiring from his job at Volkswagen in less than a year, and Frank is hopeful that he will then join him for some late-night viewings.

On Thursday in London, though, Frank will not need an alarm clock, and he will not need his students to stay mum.

“My heart is beating just thinking of it,” Frank says. “When I’m in London, I will probably sit there like a child, ‘Kyrie! Kyrie!’

“But now I can see my brother’s role, and now everyone knows what he can do. What he’s doing is exactly like what he was doing in Germany, and this for me is a surprise. The other NBA teams have superstars like LeBron James, but Daniel is doing the same thing as in the past, and it is amazing to me.”

Adam Himmelsbach can be reached at adam.himmelsbach@globe.com. Follow him on Twitter @adamhimmelsbach.