Kristin Cavallari has transformed into "a different person" since becoming pregnant.

The reality TV star and her Chicago Bears football player fianc Jay Cutler announced they are expecting their first child last month.

Kristin seems to be taking the news extremely well, as her entire demeanour has altered for the better.

"She's like a different person," a friend told Us Weekly magazine. "Calm and happy."

Kristin is getting ample support from her beau as she carries their baby. Jay has been attending to her every need.

"Jay treats her like a queen," the source continued. "He worships her."

Although Kristin and Jay are excited about expanding their family, the pair are less enthusiastic about wedding planning.

"I'm not even looking for a wedding dress right now," Kristin told Celeb Buzz this week. "I'm pregnant! I'm not going to go try on wedding dresses."

Kristin and Jay got engaged last April after a whirlwind romance. They split in July, with Kristin then confirming the wedding was back on in November.

The pair's baby is due in late summer.