The 38-year-old, who is dad to one-year-old Luna with Teigen after the couple went through IVF, said he didn’t see it coming.
Speaking to The Sun for his Bizarre guest edit, Legend said: “You’re not emotionally prepared for someone that’s going through a dark time as you’re welcoming this new life.
“When you don’t understand what’s happening, it’s a bit challenging to figure it out and you don’t know if it’s something you’ve done or some other reason why she’s not feeling well.”
However, Legend said once he started to understand what Teigen was going through and why, he was able to adjust to help her.
“It’s a chemical thing that happens to a lot of people after giving birth and there are ways to treat it and deal with it,” he added.
“So many people go through this - I think it was good for her to talk about it.”
Legend said Teigen is already “doing better” from when she wrote the open letter to reveal she had been suffering.
He added that they’re excited to have more kids - three or four in total.
Teigen wrote a candid essay about her mental health for the April 2017 issue of Glamour magazine.
“I had everything I needed to be happy and yet, for much of the last year, I felt unhappy,” she wrote. “I just didn’t think it could happen to me. I have a great life. I have all the help I could need: John, my mother, a nanny.
“But postpartum does not discriminate. I couldn’t control it.”
Teigen said she wanted to write the open letter to friends and employers to explain why she had been so unhappy.
Read Teigen’s full open letter here.
For information and support:
Mind: A mental health charity there to make sure no one has to face a mental health problem alone. Call: 0300 123 3393.
Pandas Foundation: Charity to support and advise any parent who is experiencing a perinatal mental illness. Call: 0843 28 98 401.
Mothers for Mothers: A postnatal depression support group with information and peer advice. Call: 0117 975 6006.
PNI: A website run by women who have suffered from postnatal illnesses to share personal experiences and offer support.