Billionaire Elon Musk is known for many things—like his revolutionary ideas, brash management style and controversial tweets. Being a man of empathy is not among them.

But buried in court records, a gentler, grieving father has emerged. In emails exchanged with the father of a teen who died in a fiery Tesla crash in 2018, Musk says “there’s nothing worse than losing a child.”

The thread of messages spanning almost seven weeks offers a rare glimpse into Musk’s personal involvement in customer relations around a horrific accident. He even brings up his own loss, one he has rarely discussed in public.

“My firstborn son died in my arms. I felt his last heartbeat,” Musk wrote, referring to his son Nevada Alexander Musk who died when he was 10 weeks old.

He was addressing James Riley, whose son, Barrett, was at the wheel of a Tesla Model S on May 8, 2018, when he lost control at 116 miles per hour and crashed into a concrete wall of a house in Fort Lauderdale, Florida. The car was engulfed in flames. Barrett Riley and his friend sitting in the passenger seat were both killed.

The email exchange is contained in a court filing submitted this month in a wrongful death lawsuit involving a different Tesla crash. The lawyer in that case is trying to persuade a judge to order Musk to submit to questioning about Tesla’s Autopilot assisted-driving feature.

Musk goes as far as fulfilling Riley’s request that the car company tweak a computerized feature to make it easier for parents to control the maximum speed a Tesla will go.

In June 2018, Tesla sent out a software update to its speed limit feature that would let drivers set the maximum speed between 50 mph and 90 mph through the car’s smartphone app or user interface through a four-digit PIN. Language in the owner’s manual was updated to say the feature was dedicated in the memory of Barrett Riley.

“I’ve never asked for acknowledgment for anything in my life, but it would be nice to acknowledge that Barrett and Edgar’s loss led to the enhanced safety of others,” Riley wrote to Musk on May 31, 2018.

Two days prior, Musk told Riley that Tesla “is doing everything we can to improve safety. My friends, family and I all drive Teslas, and even if they didn’t I would still do everything I could.”

Almost two years after the email exchange, Riley filed a product liability suit against Tesla in a Florida federal court. His Tesla vehicle’s lithium-ion batteries “burst into an uncontrollable and fatal fire” after the crash, according to the complaint. “Barrett Riley was killed by the battery fire, not by the accident,” he said.

Riley asked Tesla two months before the accident to install a speed limiter device in its car for his son’s safety, but it was removed without permission when the car was taken to Tesla to be serviced, according to the complaint.

If not for Tesla’s negligence, the limiter would have prevented the accident and “Barrett Riley would be alive today,” according to the complaint.

Tesla didn’t respond to a request for comment.