Ellie Kemper has given birth to a baby boy.

The 39-year-old actress - who is best known for starring on 'Unbreakable Kimmy Schmidt' - has taken to Instagram to announce that she and her husband Michael Koman welcomed their second child into the world on September 5.

Ellie wrote: ''Happy 1-Month Birthday to our baby boy, Matthew! He has inherited his dad's brown hair and his mom's desire to be carried around all day in a baby sling. He's a good boy. (sic)''

Ellie - who also has a three-year-old son called James - made a conscious effort to keep her first pregnancy a secret, hiding the news from her co-stars while shooting 'Unbreakable Kimmy Schmidt'.

However, the actress did confide in her producer Tina Fey as soon as she found out.

She said at the time: ''We had a table read, and my character is supposed to be on a rollercoaster ... It was still very early on, but I felt like a pregnant lady on a rollercoaster was not ideal so I had to tell my boss, Tina Fey. She knows every secret. I told her before I told my mom.''

After telling Tina, the pair decided to conceal her pregnancy by telling everyone on set she'd suffered a back injury, meaning she couldn't go on the rollercoaster.

However, Ellie found the lie harder to pull off than she expected.

She explained: ''I could not act like I had a back injury.

''I'm an actress, presumably. It was so [hard]. Someone asked, 'What's wrong?' and words escaped me. I'm like, 'I sprained my spine.' You can't sprain your spine! You can't do that!

''I kept forgetting I had [a back injury] so I kept doing things someone with a back injury can't do. They'd say 'Lunch!' and I'd like leap up and do cartwheels to catering. You're not supposed to do that!''