In her new book out Tuesday, Ivanka Trump thanks first lady Melania Trump for her "support and friendship."

"Melania, you are an unbelievable mother with a heart of gold. You give generously of your time and attention and I appreciate your support and friendship," the first daughter writes in Women Who Work.

Ivanka also gushed over Melania in a tweet on the first lady's birthday last week.

"Happy birthday to our First Lady (and my incredible step-mom!) Melania Trump," she wrote. "A wonderful example of kindness and grace for us all!"

Ivanka's adoration of her father's third wife comes after Vanity Fair last week reported that sources have "observed a frostiness between the two."

A source close to Ivanka described the relationship as "fine." A spokeswoman for Melania said "Ivanka and Mrs. Trump have always shared a close relationship, and that continues today."