United Airlines CEO Jeff Smisek said in a letter to Lufthansa on Thursday that United stands in solidarity with the parent airline of Germanwings, which suffered a devastating crash in the French Alps that killed all 150 on board in March, USA Today reports"On behalf of the entire United team, I want to reach out to our colleagues at Lufthansa and Germanwings to express our support during these toughest of times," Smisek wrote.

"Everyone at United grieves for the victims of the tragedy at Germanwings on March 24th, and our thoughts are with the friends and families of those on the flight, as well as with all of you," the letter continued. "We are deeply shocked by this senseless and cruel act, committed by an isolated individual."

The relationship between the two airlines goes a long way back: Both United and Lufthansa were two of the five founding members in 1997 of the worldwide Star Alliance, the world’s largest global airline alliance group that now has 27 major airline members.

Smisek also highlighted Lufthansa’s “safety culture,” bringing attention to the fact that the German carrier had an impeccable safety record before the crash of Germanwings Flight 9525.

Here's the full text of the letter:

April 2, 2015

To our colleagues at Lufthansa and Germanwings:

On behalf of the entire United team, I want to reach out to our colleagues at Lufthansa and Germanwings to express our support during these toughest of times.

Everyone at United grieves for the victims of the tragedy at Germanwings on March 24th, and our thoughts are with the friends and families of those on the flight, as well as with all of you. We are deeply shocked by this senseless and cruel act, committed by an isolated individual.

We are proud of the partnership we have had with Lufthansa for more than two decades, and we deeply admire your safety culture. We know that Lufthansa's training and safety standards are among the highest in our industry, and that you work hard to fulfill your commitment to your passengers.

Please know that all of us at United continue to keep the Lufthansa and Germanwings team in our hearts and in our thoughts.

Sincerely,

Jeff Smisek