The "Flip or Flop" star, who's pregnant with the couple's first child together, decorated the antique gray sports car with a big red bow.
Her excited hubby wasted no time sharing a photo of the car on Instagram.
"OMG!!!! Woke this morning 40 years older and the wife asked me to go outside and sign for a ping pong table!!! And THIS 1958 Porsche 356A was sitting there with a BOW!!" he gushed in the caption.
"Needless to say I was speechless! I still am!!! Birthdays are about getting socks and shower gel! I’m still coming to terms with it!" he wrote, adding jokingly, "Car has aged way better than I have!"
The self-described "car guy" has made a career of hosting TV shows dedicated to the love of fine automobiles. He's currently the host of the British series "Wheeler Dealers."
Ant also marked his milestone birthday by sharing an adorable photo of himself as a little boy, writing, "Where have the past four decades gone?"
His caption soon got more sentimental as he paid tribute to his loved ones.
"I'm incredibly lucky to be where I am, with who I am, doing what I am. I know for sure I am right where I should be! And I am excited for where I am heading! Supported by my family, my friends and those brave enough to remain fun, eccentric, bonkers and crazy! As a father that’s what I teach my beautiful children!" he sweetly added.
As for Christina, 35, she shared a festive photo of the lovebirds celebrating Ant's big day together. "40 never looked so good!!" she gushed in the caption.
"I love you my husband, best friend, baby daddy. You complete me," she added. "Happy 40th!! Cheers to doing the next 40 together."
Joining them at the ceremony were Christina's kids, Taylor, 8 and Braden, 3, with ex-husband Tarek El Moussa, and Ant's children Amelie, 15, and Archie, 12, with his ex-wife, Louise Anstead.