This is devastating.
The 31-year-old revealed, "After four years of challenging behavior and aggression that could not be treated with training or medication or consistent loving dog ownership, Lamby went to live at an amazing professional facility in Los Angeles."
She continued, "Lamby suffered terrible abuse as a pup that made having him in a typical home environment dangerous to him and others — we needed to be responsible to ourselves, our neighbors, and especially our beloved boy."
Dunham adopted Lamby from the Brooklyn animal rescue BARC, and he even has his own Instagram account with more than 17,500 followers. Despite giving him up in March, Lena still posts on it.
In 2014, the pup made headlines when Lena posted a photo of her bloody underwear to social media because he bit her, which brought about concerns from fans.
After just two months of having the pooch, Dunham published a detailed piece for the New Yorker.
She wrote, “Tears stream down my face. What have I done? We had such a nice life. The first real comfort I’ve known in so long. Nights were quiet and sweet, and we slept until whatever o’clock we wanted, then sat on the couch in our underwear and planned the day.” Nonetheless, she vowed to take care of the troubled dog. “‘I’m not going anywhere,’ I tell Lamby,” she wrote.
But apparently his challenging behavior ultimately became too much.
In Wednesday's Instagram post, the star encouraged fans in a similar situation not to send their pups back to the shelter.
"Please know it's possible to responsibly re-home your rescue rather than sending them back into the shelter system. It can require patience, diligence and often a financial contribution but there are solutions that leave everyone happy and safe."
Luckily, she has two other furry friends who are helping her through the trauma — Susan and Karen — who she adopted earlier this year.
In fact, at just six months old, they already made their debut in the spotlight after appearing on The Tonight Show Starring Jimmy Fallon in February.
"Susan and Karen will never be my first loves, but they are fuzzy and hilarious stuffing for the hole Lamby left and we cherish them deeply," she said.
Our hearts go out to you, Lena!
Scroll through our gallery below for photos of Lena's amazing weight loss transformation!