Kate and Jon Gosselin Wish Twins Mady and Cara a Happy 18th Birthday

Kate Gosselin and Jon Gosselin
D Dipasupil/Getty Images for Extra / Dave Kotinsky/Getty Images

The former couple's sextuplets turned 14 back in May.

Cara and Mady Gosselin are officially adults!

The 18-year-old twins celebrated their milestone birthday on Monday and their parents, Jon and Kate Gosselin, took to Instagram to mark the occasion. Fans got their first look at the twins -- and their sextuplet siblings, who are now 14 -- when Jon & Kate Plus 8 premiered in 2007.

Jon, 41, sent his oldest daughters a message of love on his Instagram account.

Kate, 43, wrote a lengthy note to her girls alongside pics of the preparations for their party.

"Getting ready.........it’s a BIG busy day here! More to come.... HAPPY 18th Birthday, Cara and Madelyn!" Kate wrote. "There are no words to describe how proud I am of you both. Despite the many turbulent times you’ve had to deal with so far in life, you have emerged as wise, level headed, reasonable, forgiving, loving, kind and absolutely brilliant ADULTS!"

The proud mom continued, "I can say that I’ve poured endless love into you and fought tooth and nail for the best for you, but I cannot possibly take credit for the truly wonderful humans (adult humans!) you have become! You will thrive in life, I am certain, and I will still be with you every step of the way going forward, continuing to guide you and love you??."

"I love you both so very very much and I wish peace, happiness and the great successes I know are coming your way!" Kate concluded. "#Turning18 #Adults #Love❤️❤️ #Happy18thBirthdayCara ???#Happy18thBirthdayMady ???"

The big birthday for the twins comes after the sextuplets celebrated their 14th birthday in May. At the time, a source told ET that Jon and Kate are "still at odds" nearly 10 years after their divorce.

"They will never agree about how to raise the children," the source said, adding that the two "absolutely despise one another and can't stand to even be in the same room."

Watch the video below for more on the Gosselin family: