According to the Japanese newspaper Asahi Shimbun, Masako, who has been suffering from a stress-induced adjustment disorder for nine years, is said to have greatly improved after speaking to Maxima earlier this year.
In April Masako made her first official overseas visit for 11 years to attend King Willem-Alexander's inauguration in Amsterdam after his wife Maxima requested that she attend.
Masako and Naruhito at the Dutch inauguration
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On hearing that the Japanese royal was initially reluctant to make the journey Maxima personally phoned Masako and convinced her to come.
"The new king invited Naruhito [Masako's husband] in person when they met at a conference held in New York in March," reports Asahi Shimbun. "Maxima requested Masako's attendance over the phone.
"The conversation with the queen about the trip to Holland served to strengthen her [Masako's] self-esteem."
The Dutch and Japanese royal families have been close for many years. In 2006, two years after Masako's diagnosis, the then Queen Beatrix invited the family for a two-week holiday at her private estate, Het Loo Palace, in Apeldoorn.
Many royal watchers have said that Beatrix sympathised with Masako's condition given that her own husband, the late Prince Claus, suffered with severe depression
During the holiday the two families were pictured laughing and smiling together and Masako's daughter Aiko happily played with Maxima and Willem-Alexander's eldest daughter Catharina-Amalia.
The families together during Masako and Naruhito's holiday in 2006
Earlier this week, to mark her 50th birthday, Masako wrote a two-page public statement that hinted at a brighter future.
The mother-of-one vowed to "continue efforts to make a full recovery" from her long-term illness, adding "I feel strong gratitude toward the many people who helped me get to where I am now."