"He's deeply saddened by Khloé filing for divorce," a source exclusively tells E! News. "He knew it was coming and it was only a matter of time. He felt like he gave his all to try and save the marriage, but ultimately he wasn't able to."
Khloé cited irreconcilable differences as the reason for the split, but the two had been having issues for some time, no small portion of which was Lamar's battle with substance abuse and his arrest for DUI on Aug. 30.
They had been living mainly apart since the summer while also going to counseling and otherwise trying to work things out.
"There will always be a place in his heart for Khloé," the source adds. "He will always love her and her family. She has decided and there is nothing more he can do. He has to accept that."
Lamar spent the week before Thanksgiving training on the University of Rhode Island campus for his hoped-for return to the NBA. He then spent the holiday in L.A. with his father. He and Khloé also spent their fourth anniversary back in September apart from each other.
We've been told that Lamar, aside from physically toiling to get himself back in playing shape, has been working hard on his relationship with his father, from whom he's been periodically estranged, and his two children.
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Back in September, he called his dad his "downfall" in a long Twitter post and referred to the family he married into as a "blessing."
"His own demons may be the ONLY thing he gave 2 me," Lamar wrote. "He disrespecting the ONLY FAMILY that has loved me without expecting anything in return. They are the ONLY ones that have been here consistently 4 me during this dark time."
"He wishes her and her family all the best in the future," our source told us today. "He'll never stop loving her."
Lamar was spotted in Studio City, Calif., on Wednesday, while Khloé was photographed hitting the gym today, part of her usual routine. Though she continued to wear the 12.5-carat diamond ring that Lamar gave her for months amid rumors of marital trouble, she was without it her last few appearances in public.
Khloé's most recent post to Instagram came yesterday, a note reading: "I am strong because I've been weak. I am fearless because I've been afraid. I am wise because I've been foolish."