Alexander Stubb admitted it was “sad” that Britain voted to Leave the European Union but said he was “rooting” for the UK.
The former politician added that he hopes negotiations will be “civil” to ensure both sides get a good deal.
Speaking to Sky News, he said: “I think the sad thing with the Brexit is that it is a lose lose proposition for everyone.
“Usually I am a win win person but this time round the UK is going to lose and Europe is going to lose.
Alexander Stubb claimed Brexit would be lose-lose for the UK and EU
“I do hope that we can have a civil set of negotiations and we will be out of these negotiations with a fairly good result.”
Theresa May said she would fight for a good trade deal with the EU after announcing that she would pull Britain out of the single market.
The former Finnish prime minister claimed it was impossible for the UK to receive a better deal from the EU than Britain currently has.
He added: “You know I am married to a Brit so I am rooting for the UK, even in this difficult case.
Brexit is a lose lose proposition for everyone
“But to be quite honest that is what EU membership is all about. When you are in the club you get the benefits of membership, you enjoy the four freedoms, you get to pay a little bit, sometimes you get a little bit back.
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“You get to sit around the table where the decisions are made.
“But when you decide to Leave the EU you are going to be worse off.
“That is what the UK voted for and in that sense I think it’s quite honest and straight forward for Donald Tusk to say that.
In pictures: Theresa May meets with EU's Tusk Thu, April 6, 2017
The two leaders held talks on Brexit negotiations
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European Council President Donald Tusk gestures to members of the media as he leaves 10 Downing street after talks with British Prime Minister Theresa May in central London
“Britain is going to be much worse off outside. I’m sorry about that but that is just reality.”
Mr Stubb suggested that the negotiations would have their “ups and downs” throughout the 24-month Brexit process, but urged both sides to be focused on achieving a good deal.
He said: “It is going to be confrontational, it is going to be difficult.
“At the end of the day we will survive and there will be a deal.”