Jessica Simpson celebrated her fiancé's birthday in Los Angeles on Friday night (13.09.13).

The 33-year-old star was spotted enjoying an early dinner with Eric Johnson, with whom she has two children, a 15-month-old daughter, Maxwell, and a two-month-old son, Ace, at Japanese restaurant Benihana in Santa Monica, California, before ditching her designer heels to enjoy a night of bowling with the former NFL star and their friends at the nearby AMF Bay Shore Lanes Bowling Alley.

Following the bash, Jessica tweeted a picture of her with Eric and wrote: ''Birthday weekend!!! I love you with everything and more and more and more....''

The fashion designer recently revealed she and Eric, who will turn 34 on Sunday (15.09.13), are closer than ever since having children.

She said: ''My relationship with Eric has only grown stronger with the additions to our family. I love seeing him as a dad. I feel like I reached a new level of love for him and I didn't think I could love him any more than I did already. Becoming a parent is such a unique and profound experience and doing it together has brought us even closer.''

She added: ''Eric is incredible. I can safely say he has changed way more diapers than I have. Any time either of our babies needs anything, Eric is right there. I am so lucky to have him.''

The couple are reportedly in the final stages of planning their wedding, as they want to get married before they have any more children.

A source previously said: ''[Jessica] was telling friends she wanted to get married a few months after the baby is born.''