“It was and will forever be, one of the happiest days of my life,” she writes in the caption of a photo of the two of them taken Monday. “My heart is broken. My soul aches. I am lost. He is the greatest love of my life. He is my best friend.”
She continues: “As we separate, and attempt to find our footing through life, all I can hope for us is that we both find happiness within ourselves.”
“I love you,” she adds. “You’ll always have my heart. You’ll always be my first husband.”
King told PEOPLE in May 2016 that “being in love has changed me.”
“As a single girl, as ‘Ex’s and Oh’s,’ Elle King, that person spent most of her nights in bars until the lights came one,” she said. “I can out-drink and out-party the best of ’em, but it’s nice to not want or need to do that anymore. It’s really very comforting.”
In July 2016, King dropped by the iconic N.Y.C boutique Kleinfeld Bridal to track down a wedding gown, and PEOPLE was there for the filming of the episode, which aired on TLC.
RELATED VIDEO: Singer Elle King Says She ‘Skipped Out’ On Her Wedding in Favor of Rock Show
“I tried on maybe six or seven gowns, but none of them mattered,” she told PEOPLE the day of the fitting of the number she chose for her April 2017 ceremony. “I saw Randy bring it in, and I remember being like, ‘Something about it is special.’ My mom was like, ‘Baby, that’s it.’ I burst out into ugly tears, and then we went out, and I said yes to the dress, came back in, and my mom ugly-cried, so I knew it was truly ‘the one.'”
Despite having picked a wedding gown, the singer said she “skipped out” on her wedding in favor of a rock show in what would have been her wedding weekend.
“Please be respectful of our emotions and out space during this time,” King writes in the Instagram post. “Everybody thought I lost my mind and I did. So, be kind.”