Chester Bennington and Chris Cornell: Inside the close bond they shared

— -- The music world lost two rock icons -- Chris Cornell and Chester Bennington -- within months of each other.

Bennington's death is being investigated as "a suicide by hanging," a spokesman for the Los Angeles County Coroner's office told ABC News on Friday.

A final cause of death won't be confirmed until after the autopsy is completed, according to Ed Winter, a spokesman for the coroner's office.

The former lead singer of Linkin Park was 41 years old.

In May, former Soundgarden frontman Cornell took his own life, according to the Wayne County Medical Examiner's office.

Bennington died on what would have been Cornell's 53rd birthday.

In the wake of their deaths, fans have highlighted the close bond the two rockers shared, posting videos of their performing together as well as their past tributes to each other, including an open letter Bennington posted at the time of Cornell's death.

Cornell and Bennington became close when they toured together in the mid-2000s, just a few years after Linkin Park hit it big with its debut album "Hybrid Theory." By then, Cornell had been a rock icon for the better part of a decade. Soundgarden had played a major role in the grunge movement during the '90s.

During that 2007 to 2008 tour, the two singers' chemistry on stage was undeniable.

In one of the videos fans re-posted to social media on Thursday, Cornell and Bennington sing the Temple of the Dog song "Hunger Strike," with Bennington's filling in for the vocals originally done by Pearl Jam's Eddie Vedder. There is a full embrace between the two as Bennington walks out for the second verse of the song.

During the same tour, Cornell returned the favor, joining in on Linkin Park's hit "Crawling," among other duets.

When Cornell died on May 18, Bennington wrote an emotional open letter to his friend.

"Thoughts of you flooded my mind and I wept. I’m still weeping, with sadness, as well as gratitude for having shared some very special moments with you and your beautiful family. You have inspired me in many ways you could never have known. Your talent was pure and unrivaled. Your voice was joy and pain, anger and forgiveness, love and heartache all wrapped up into one," he wrote. "I suppose that’s what we all are. You helped me understand that ... I can’t imagine a world without you in it. I pray you find peace in the next life. I send my love to your wife and children, friends and family. Thank you for allowing me to be a part of your life."

On the night of May 18, Linkin Park performed on "Jimmy Kimmel Live," where Bennington opened the performance with a tribute to his late friend.

"We were going to come out and play 'Heavy' first," Bennington told the audience. "In light of our dear friend Chris Cornell passing away, we decided to play our song, 'One More Light' ... We love you Chris."

"Who cares when someone's light goes out ... Well, I do," Bennington sang before bowing his head down at the end of the song.

Linkin Park bandmate Mike Shinoda spoke to Radio.com days after the "Jimmy Kimmel" performance and explained how much Cornell's death had affected Bennington.

"When we were doing a sound check, Chester couldn’t even make it through the song, he was getting halfway through and getting choked up. And even when we did play the whole song, and it was live on TV, or taped for film for TV, he kind of just stopped like towards the end like he missed the last couple lines, just couldn’t finish the song," Shinoda said at the time.

Bennington was also the godfather of Cornell's son and sang at Conrnell's memorial service, the Associated Press reported.

The men's families have remained close as well.

On Thursday, Cornell's widow, Vicky, tweeted, "Just when I thought my heart couldn't break any more.....I love you" around the time that Bennington's death was confirmed.

“The Cornell family is overwhelmed by the heartbreaking news about Chester Bennington which tragically comes so soon after their family's own loss,” said a Cornell family spokesperson. “They open up their loving arms to Chester’s family and share in the sorrow with all those who loved him."

The Associated Press contributed to this report.