Jamie Lynn Spears is pregnant.

Jamie Lynn Spears (c) Instagram

Jamie Lynn Spears (c) Instagram

The 26-year-old actress has taken to social media to publicly announce her and her husband, Jamie Watson, are due to have "another big milestone" in 2018 as they are expecting their first child together.

Alongside a photograph of the former 'Zoey 101' star with her spouse and her nine-year-old daughter Maddie - who Jamie has with her former partner Casey Aldridge - which was posted on her Instagram account, she wrote: "Looks like we are starting off 2018 with another big milestone...sooo happy to announce that Maddie is FINALLY going to be a big sister (sic)."

In the heartfelt post Jamie revealed 2017 has been a difficult year for her as her child nearly drowned in an ATV accident.

She continued: "2017 was filled with some of the biggest challenges of my life, as well as some of the biggest blessings (sic)."

And over the last 12 months Jamie decided to "lay low" to focus on herself and her career.

She added: "So I made a choice to lay low this year to focus on truly becoming my best self as a person and as an artist. (sic)."

Jamie has teased she has been working on new music, which she "can't wait" to share with her fans.

She said: "During that time, I continued working on my music and telling my story, which has created some of my most honest work and I CANT wait to share that with you all very soon.(sic)."

Although 2017 has been filled with "challenges" and "blessings" for Jamie, she thinks the next year will see her achieve "many milestones both personally and professionally".

She concluded her post: "2018 is going to be filled with many milestones both personally and professionally. I appreciate each of you for your patience and support through it¬ all. 2018 has a lot coming, so GET READY........ #12DaysofJLS (sic)."

Jamie has also shared the post on her Twitter account.

And Jamie's older sister Britney Spears has since taken to social to congratulate her sibling.

The 36-year-old singer re-shared Jamie's tweet and wrote: "Maddie is going to be the best big sister!!! So happy for you @jamielynnspears!!!! Love you all sooo much!!!(sic)."