Josh and Anna Duggar, with their two older children Mackynzie and Michael. Credit: TLC

Keep counting! The eldest son of the Duggar family, Josh Duggar, is going to be a father once more. 

Josh's wife Anna Duggar took to Twitter on Tuesday evening, Dec. 2, to announce that she is pregnant with her fourth child. 

"We are so excited to announce... we're pregnant! #4andCounting #BlessingfromTheLord @joshduggar #19Kids," she wrote. 

Josh and Anna, both 26, married in September 2008 and quickly got to work on mirroring the massive brood led by Josh's famously conservative parents Jim Bob and Michelle Duggar. While Josh and his 18 siblings all have names that begin with the letter "J," he branched out slightly, using the letter "M" for his own growing family.

The happy couple welcomed their first child, daughter Mackynzie Renée, in October 2009, going on to introduce sons Michael James in June 2011 and Marcus Anthony in June 2013. Anna and Josh have yet to announce whether their latest addition will be a Melissa or Mark. 

The religious pair also teased the exciting news in a clip from TLC. 

"This time of the year, there's so many things we're thankful for," Josh says in the video, surrounded by his pregnant wife and three children. "From my sisters getting proposed to and married, to all the fans who are watching at home."

Anna then chimed in, spilling, "One of the things we're really thankful for this season, is that we're expecting!" She added to TLC that she is nine weeks pregnant, a few months behind her sister-in-law Jill Duggar, who announced her own pregnancy news this past August. 

"I'm having a lot of morning sickness so it is difficult, but it's good because I know good things are happening," Anna continued. "After Ben and Jessa's wedding, we were still visiting with the family in Arkansas, and that was really exciting to get to share with the family the exciting news."

In addition to the congratulations from their family members, the couple's TLC comrade Bill Klein of The Little Couple tweeted his well-wishes to the expectant parents on Tuesday, writing, "Congrats Josh and Anna! Just saw you guys are expecting!! Awesome!"