"The whole family comes in with a homemade cake and very fun gifts to the bed, and it is the world's loveliest start to the day," she said during an interview following her 40th birthday, which took place on Sunday.
"Haakon bakes a cake on my birthday every year, but you must not tell anyone."
The Crown Princess said the prince had bought her a year's gym membership as a present, following gifts of tents and bicycles and other sports equipment in previous years.
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Mette-Marit, a single mother with a rebellious past, was a controversial figure at the time of her engagement to Haakon in 2001, but has won the nation's respect with her lively personality and humanitarian work.