The wedding will take place in the Royal Palace church (Slottskyrkan) in Stockholm, newspaper Expressen revealed today.
"It was expected that we would announce a date. I can confirm that we have decided on June 8th," Royal Court spokesman Berrtil Ternert told the TT news agency.
"We cannot say more at this point. We will have more information a bit later," added Ternert.
The couple decided on the place and date for the wedding after consulting King Carl XVI Gustaf and Queen Silvia, Expressen reports.
The timing of the announcement is not surprising, according to Roger Lundgren, editor of Kungliga Magasinet, a publication focused on news about royalty.
"They are gathered for Christmas and were due to set a date so the announcement was expected," Lundgren told TT.
He added that the choice of venue was evident, too. The Storkyrkan church, where Crown Princess Victoria married, is too big, said Lundgren.
"Victoria's wedding was three times bigger than Madeleine's will be. This is a more intimate wedding."
Princess Madeleine and Chris O'Neill exchanged engagement rings in New York in the autumn but kept the engagement secret for one month.
The engagement was officially announced in October.
News of Madeleine and O'Neill's relationship first surfaced in media reports in early 2011 and in February of this year, the Royal Court confirmed that Madeleine and O'Neill had been living together in his Manhattan apartment since November 2011.
O'Neill made his first official appearance with the royal family in Stockholm at the May 2012 baptism of Princess Estelle.
While in New York, the princess has been working with the World Childhood Foundation, a charity for marginalized children set up in 1999 by her mother.
London-born O'Neill, 38, works in finance and is currently a partner at Noster Capital, which has offices in New York and London.
The couple said O'Neill proposed in early October after asking the King's permission.
"It was a very romantic and intimate proposal, but more details about the proposal we want to keep to ourselves," Madeleine said.
She added that they plan to continue living in New York for the time being.
Madeleine's older sister is Crown Princess Victoria, 35, who married Daniel Westling in June 2010. They have a daughter, Princess Estelle, born in February.
She also has a brother, Prince Carl Philip, 33.
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